text:
How do I defend against players who keep pawn pushing in the Sicilian?
I recently played a Sicilian as black, defending against a pawn storm.
Here is the game:
[Event "Rated Classical game"]
[Site "https://lichess.org/ZMFC6dP4"]
[Date "2018.11.11"]
[Round "-"]
[White "crowlol"]
[Black "JushBJJ2"]
[Result "1-0"]
[UTCDate "2018.11.11"]
[UTCTime "11:50:56"]
[WhiteElo "1608"]
[BlackElo "1644"]
[WhiteRatingDiff "+12"]
[BlackRatingDiff "-11"]
[Variant "Standard"]
[TimeControl "900+15"]
[ECO "B20"]
[Opening "Sicilian Defense: Bowdler Attack"]
[Termination "Normal"]
[Annotator "lichess.org"]

[FEN "..."]
1. e4 c5 2. Bc4 { B20 Sicilian Defense: Bowdler Attack } d6 3. Nf3 Nf6 4. Ng5?! { (0.00 → -0.65) Inaccuracy. Best move was Nc3. } (4. Nc3 a6 5. d4 cxd4 6. Nxd4 b5 7. Bb3 e6 8. O-O Qc7) 4... e6 5. d3 Nc6 6. Bf4 Be7 7. Nf3 O-O 8. h3 Bd7?! { (-0.86 → -0.30) Inaccuracy. Best move was d5. } (8... d5 9. exd5 exd5 10. Bb3 a5 11. a4 Bd6 12. Bxd6 Qxd6 13. O-O Nh5 14. Nc3 Nf4 15. Kh1) 9. g4? { (-0.30 → -1.60) Mistake. Best move was Nc3. } (9. Nc3 Nd4 10. a4 Nxf3+ 11. Qxf3 a6 12. O-O Bc6 13. Rfd1 d5 14. Bb3 h6 15. exd5 exd5) 9... e5?! { (-1.60 → -0.81) Inaccuracy. Best move was d5. } (9... d5) 10. Be3 Be6 11. b3? { (-0.80 → -1.87) Mistake. Best move was Bb3. } (11. Bb3 c4 12. Bxc4 Bxc4 13. dxc4 Nxe4 14. Qd3 f5 15. gxf5 Nc5 16. Qd5+ Kh8 17. Bxc5 dxc5) 11... Qa5+? { (-1.87 → -0.63) Mistake. Best move was d5. } (11... d5 12. exd5 Nxd5 13. Bd2 f5 14. Nc3 Qd7 15. Qe2 Ndb4 16. O-O-O Bxc4 17. dxc4 e4 18. Nxe4) 12. Bd2 Qd8 13. Ng1? { (-0.68 → -2.73) Mistake. Best move was O-O. } (13. O-O a6) 13... Bxc4? { (-2.73 → 0.04) Mistake. Best move was d5. } (13... d5 14. exd5 Bxd5 15. Rh2 e4 16. Nc3 Qd6 17. f4 exf3 18. Rf2 Bxc4 19. bxc4 Nd4 20. Nxf3) 14. bxc4 Re8 15. g5 Nd7 16. h4 a6 17. Qg4? { (0.44 → -1.28) Mistake. Best move was a4. } (17. a4) 17... Qc8?! { (-1.28 → -0.42) Inaccuracy. Best move was b5. } (17... b5 18. Ne2 bxc4 19. dxc4 Nd4 20. Na3 Nf8 21. c3 Nxe2 22. Kxe2 Qa5 23. Nc2 Rab8 24. Kf1) 18. h5?! { (-0.42 → -1.21) Inaccuracy. Best move was Nc3. } (18. Nc3 b5 19. Nd5 bxc4 20. dxc4 Rb8 21. Nf3 Nd4 22. Kf1 Nxc2 23. Rd1 Nb6 24. Qxc8 Nxc8) 18... Nb6? { (-1.21 → 0.23) Mistake. Best move was b5. } (18... b5 19. Kf1 Nd4 20. Nc3 bxc4 21. Rc1 Nb6 22. Qg3 Rb8 23. Nge2 Qe6 24. Rg1 cxd3 25. cxd3) 19. Qg3 Nd7?! { (-0.21 → 0.71) Inaccuracy. Best move was Nd4. } (19... Nd4 20. Na3 Qc6 21. g6 Qa4 22. c3 Qxa3 23. cxd4 Qb2 24. Rc1 cxd4 25. h6 hxg6 26. hxg7) 20. g6?! { (0.71 → -0.13) Inaccuracy. Best move was Nc3. } (20. Nc3 b5 21. Nd5 bxc4 22. Nf3 Nf8 23. dxc4 Nb4 24. Kf1 Nxd5 25. cxd5 Rb8 26. h6 gxh6) 20... Rf8? { (-0.13 → 1.22) Mistake. Best move was Nd4. } (20... Nd4 21. Na3) 21. gxh7+ Kh8 22. h6? { (1.07 → 0.05) Mistake. Best move was Nc3. } (22. Nc3 Nd4 23. Rc1 Ne6 24. Nge2 Qd8 25. Rb1 b5 26. cxb5 axb5 27. Rxb5 Bg5 28. a4 Bh6) 22... g6 23. Bg5? { (0.10 → -1.47) Mistake. Best move was Nc3. } (23. Nc3 Nd4 24. Rb1 Nf6 25. Bg5 Nxc2+ 26. Kd2 Nd4 27. Qh4 Qd8 28. Rxb7 Ne6 29. f4 Nxg5) 23... Qd8?! { (-1.47 → -0.81) Inaccuracy. Best move was Bxg5. } (23... Bxg5 24. Qxg5 Nd4 25. Kd1 b5 26. Nd2 Ne6 27. Qh4 b4 28. a3 a5 29. Ngf3 Qd8 30. Qxd8) 24. Be3?! { (-0.81 → -1.52) Inaccuracy. Best move was Bxe7. } (24. Bxe7 Qxe7 25. Nc3 Nd4 26. Rc1 Qd8 27. Kf1 b5 28. Nd5 bxc4 29. dxc4 Rb8 30. Ne2 Kxh7) 24... b5 25. Nc3 Nd4 26. Bxd4 cxd4 27. Nd5 Nf6?! { (-1.87 → -1.34) Inaccuracy. Best move was bxc4. } (27... bxc4 28. Nf3 Nf6 29. Nxf6 Bxf6 30. Nd2 cxd3 31. cxd3 Kxh7 32. Nc4 Rb8 33. Kf1 Qe7 34. Ke2) 28. Nxf6?! { (-1.34 → -1.92) Inaccuracy. Best move was Nxe7. } (28. Nxe7 Qxe7) 28... Bxf6 29. Ne2?! { (-1.92 → -2.43) Inaccuracy. Best move was Nf3. } (29. Nf3) 29... Qa5+ 30. Kf1 Qd2 31. Rc1 Qg5? { (-2.43 → -1.01) Mistake. Best move was Rac8. } (31... Rac8) 32. Qxg5 Bxg5 33. Ra1?! { (-1.33 → -1.94) Inaccuracy. Best move was Rb1. } (33. Rb1 bxc4 34. dxc4 Rac8 35. Rb4 Rc7 36. Rh3 Rfc8 37. Rf3 Rxc4 38. Rxc4 Rxc4 39. c3 dxc3) 33... Kxh7?! { (-1.94 → -1.26) Inaccuracy. Best move was bxc4. } (33... bxc4) 34. a4? { (-1.26 → -2.35) Mistake. Best move was Rh3. } (34. Rh3 Rac8 35. c3 dxc3 36. Nxc3 bxc4 37. Rd1 Rfd8 38. Kg2 Rd7 39. dxc4 Rxc4 40. Rg3 Bh4) 34... b4? { (-2.35 → -1.11) Mistake. Best move was bxc4. } (34... bxc4 35. dxc4 Rac8 36. Rh3 Rxc4 37. c3 dxc3 38. Nxc3 Rb8 39. Ra3 Bxh6 40. a5 Kg7 41. Rd3) 35. a5 Bxh6 36. Rb1 Rab8 37. f4 Kg7 38. fxe5 dxe5 39. Rb2?! { (-1.60 → -2.46) Inaccuracy. Best move was Kg2. } (39. Kg2 Be3 40. Kf3 f5 41. Rh2 Kf6 42. Ng3 Rf7 43. Ke2 Bf4 44. Rh3 Bxg3 45. Rxg3 Rh7) 39... f5 40. exf5?! { (-2.33 → -3.03) Inaccuracy. Best move was Kg2. } (40. Kg2 fxe4 41. Ng3 e3 42. Ne4 Rf4 43. Rf1 Rh4 44. Rfb1 Bg5 45. Rxb4 Rxb4 46. Rxb4 Bd8) 40... Rxf5+ 41. Kg2?! { (-2.64 → -3.31) Inaccuracy. Best move was Ke1. } (41. Ke1 Be3 42. Rb1 e4 43. dxe4 Rxa5 44. Rd1 Rc5 45. Nxd4 Rxc4 46. Nb3 Rxc2 47. Rd7+ Kf6) 41... Rg5+? { (-3.31 → -1.43) Mistake. Best move was Be3. } (41... Be3 42. Rf1) 42. Kf3?! { (-1.43 → -2.13) Inaccuracy. Best move was Kh3. } (42. Kh3 e4 43. Nxd4 Rxa5 44. c5 exd3 45. cxd3 Be3 46. Nc6 Rh8+ 47. Kg2 Rxh1 48. Kxh1 Rxc5) 42... Rf5+ 43. Ke4 Rf2 44. Ng3 Bf4 45. Rg1 Bxg3?! { (-1.34 → -0.54) Inaccuracy. Best move was Kf6. } (45... Kf6 46. Kd5 Bxg3 47. Rxg3 Rd8+ 48. Kc6 e4 49. Rxb4 e3 50. Rg1 Rxc2 51. Rb6 Ke5 52. Kc7) 46. Rxg3 Re2+ 47. Kd5 Re3?! { (-0.08 → 0.45) Inaccuracy. Best move was e4. } (47... e4 48. Rb1 Rd8+ 49. Kc5 exd3 50. cxd3 Re5+ 51. Kc6 Re3 52. Rg4 Rxd3 53. Rxb4 Kf6 54. Rb6) 48. Rxe3 dxe3 49. Rb1 Kf6 50. Re1 b3? { (0.62 → 2.04) Mistake. Best move was e4. } (50... e4 51. dxe4) 51. cxb3 Rxb3?! { (1.54 → 2.34) Inaccuracy. Best move was g5. } (51... g5) 52. Rxe3 Kf5? { (2.27 → 5.20) Mistake. Best move was Rc3. } (52... Rc3 53. Rf3+) 53. Rxe5+ Kf4 54. d4 Ra3?? { (4.00 → 7.58) Blunder. Best move was g5. } (54... g5 55. c5) 55. c5 Rxa5? { (7.21 → 10.26) Mistake. Best move was g5. } (55... g5) 56. Kd6 g5? { (8.52 → 11.30) Mistake. Best move was Rb5. } (56... Rb5 57. Re8) 57. Re8?? { (11.30 → 6.39) Blunder. Best move was c6. } (57. c6 Rxe5 58. dxe5 g4 59. c7 g3 60. c8=Q g2 61. Qc1+ Kg3 62. Kc5 a5 63. Kb5 Kh2) 57... g4?? { (6.39 → 42.68) Blunder. Best move was Rb5. } (57... Rb5 58. c6) 58. c6 Ra4 59. d5 Rc4 60. c7 g3?! { (16.97 → Mate in 15) Checkmate is now unavoidable. Best move was a5. } (60... a5 61. c8=Q) 61. c8=Q Rxc8 62. Rxc8 g2 63. Rc1 a5 64. Kc5 Ke5 65. d6 a4 66. Rg1 a3 67. Rxg2 Ke6 68. Ra2 Kd7 69. Rxa3 Kd8 70. Kc6 Ke8 71. d7+?! { (Mate in 2 → Mate in 4) Not the best checkmate sequence. Best move was Rf3. } (71. Rf3 Kd8 72. Rf8#) 71... Kd8 72. Ra8+?! { (Mate in 4 → Mate in 4) Not the best checkmate sequence. Best move was Rf3. } (72. Rf3 Ke7 73. d8=R Kxd8 74. Re3 Kc8 75. Re8#) 72... Ke7 73. d8=Q+ Ke6 74. Qe8+?! { (Mate in 3 → Mate in 4) Not the best checkmate sequence. Best move was Qg5. } (74. Qg5 Kf7 75. Ra7+ Ke6 76. Re7#) 74... Kf6 75. Rd8?! { (Mate in 4 → Mate in 4) Not the best checkmate sequence. Best move was Qh5. } (75. Qh5 Kg7 76. Ra7+ Kf6 77. Rf7+ Ke6 78. Qd5#) 75... Kg7 76. Qe6 Kh7 77. Rd7+ Kh8 78. Qe8# { White wins by checkmate. } 1-0

How do I defend against players who keep pawn pushing in the Sicilian? I really stress against these kind of players.

Pawn pushing is a well known anti-Sicilian strategy. The main problem here is that your play was too passive and you paid more than enough attention to your opponents while they were pushing their pawns. While your opponent were rushing their pawns, they allowed many chances where counterplay by you is possible yet you were focusing only on their pawns. Here are examples:
[FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
[Event "Rated Classical game"]
[Site "https://lichess.org/ZMFC6dP4"]
[Date "2018.11.11"]
[White "crowlol"]
[Black "JushBJJ2"]
[Result "1-0"]
[UTCDate "2018.11.11"]
[WhiteElo "1608"]
[BlackElo "1644"]
[ECO "B20"]
[Opening "Sicilian Defense: Bowdler Attack"]
[Termination "Normal"]
[StartPly "17"]

1. e4 c5 2. Bc4 d6 3. Nf3 Nf6 4. Ng5 e6 5. d3 Nc6 6. Bf4 Be7 7. Nf3 O-O 8. h3 Bd7 9. g4

In the above position, 9... d5 would have been very annoying for your opponent. Your opponent is now forced to play 10. exd5, placing their king in an open e-file. They won't be able to castle early then, since the kingside pawns have been advanced. Otherwise, they will lose a pawn (after say 10. Bb3 dxe4 11. dxe4 Nxe4).
Another advantage of this move is that it takes away the center from you opponent. After 9... d5 10. exd5 exd5 11. Bb3 you have decent central control, in addition to freeing the bishop such that 10... Bd6 is possible.
Moving on to the middlegame, I would say your defense was brilliant. However, instead of maneuvering the knight to the queenside, the engine suggests 18... b5, eventually starting an attack on the queenside. Obviously your plan was to free the queen, and 18... Nf8 was better in my opinion, as it puts the knight in the area where all the action is taking place.

Thanks mate, Im considering using chess stack exchange more than the lichess forums.

If you find defending stressful, then a counterattack might be a good strategy for you. Generally, if the opponent is attacking your castled king when their own king is in the middle of the board, it's often good to try to open up the center to expose their king's vulnerability. There were some points where you could have played ...d5 to help with that.
After 20.g6, one option would have been ...fxg6 hxg6 h6 and now White would have to sacrifice a bishop with Bxh6 to keep up the attack. (Of course, you'd have to make sure that the sacrifice doesn't result in some unstoppable attack before playing that move.)
But overall your defense wasn't bad. You refrained from moving those pawns in front of your king too early, which would have given your opponent's pawns a good target to attack. You survived the attack and eventually wound up with an extra pawn.

Pawn storms are a pretty standard theme in the Sicilian.  Usually, the response is to counterattack and try to checkmate them before they checkmate you.
Black almost always castles on the kingside, so that's where White's pawn storm happens. If White has castled queenside, then Black typically responds by attacking there with a pawn storm, and opening the c-file against the White King.  If White castles kingside or doesn't castle at all, then their kingside pawn storm inherently weakens their king, leaving it open to attack.


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Queen's Gambit Accepted Nc3 VS Nd2
Usually I play somewhere around move 5-Nc3 but I might start playing Nd2 more instead to get a different dynamic in the game.
Is this advised? Does this have dire consequences in QGA?

Unless you have a good reason, why would you block your own queen bishop and release tension on the important d5 square?
The idea of the gambit is to intensify pressure on the d5 square. Volunteering yourself away by Nd2 is unusual.

Assuming we're talking nbd2, it is used less but not by too much. If you want pressure on d5, you can pla Nb6, forcing the light sq bishop away and hitting d5.

Agree with SmallChess answer.  However, Nge2 ( you are talking about your Ng1 Knight, correct? ) is still problematic even if your bishop is out.  In QGA lines where Black pushes queenside pawns the Knight on c3 often likes to retreat to e2 after ..b4 where the knight is well placed to spring back into action.

Since the OP evoques the moves Nc3 or Nd2, I would infer that he is talking about his Nb1.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

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text:
Concentration during games
I've noticed that I lose sight of pieces' positions very fast during games, also, for some reason, I fail at having an "objective" view, some kind of an eagle eye, i.e I find myself concentrated on where the action is, the 3 or 4 squares related to the last move, this is obviously a default in me and would really wish to get helpful advice from you lots.

I think I am the best person to answer this question as I have come across a similar kind of situation.
I would suggest you to first focus on whether you are losing your pieces by any opponent's strategy. Don't directly play with a high level opponent . For increasing your alertness, you can play chess on computer at a lower level and then gradually increase it once you start winning. 'Chess titans', for example, on Windows 7 is an excellent game to improve firstly your alertness, then the logical skills , and finally patience. Try to analyze what is happening on the board instead of narrowing your vision to 3-4 squares. This will greatly benefit you, my friend.
Now, we turn to logical skills. The most important thing here is to predict your opponent's move and develop your strategy to make him/her fall into your trap. Try to think simple rather than complicating situations. I would also suggest you to be calculative while playing. Here I mean to say that you should be able to think what is going to happen on the board after 2-3 moves. Thereafter, increase the count. I know that it is not possible in all situations, but try to exploit the situations where it works.
Finally,  patience. Patience , in any work, is the key to success. You can also calculate and plan your next moves while your opponent is planning his/her next move. Also you can try to be ahead of your opponent in calculations. For example , if your opponent has calculated what is going to happen in the next three moves, and if you have calculated upto 4 moves, then you have an edge over your opponent.
These simple techniques have helped me in overcoming my problems and I hope these will be beneficial for you too.

Bless you mon ami!

@archaic , it is my pleasure to help you out.

The problems you're describing are common with inexperienced players, and that is only natural; the number of possible moves in the average chess position is rather large, and keeping track of everything that's going on in a position is basically impossible without guidelines and experience.
These problems (i.e. losing sight of the position of pieces/losing focus of everything except for a small region of the board) will gradually go away as you gain more experience. However there are things that you can do to actively speed up the process of improving your "eagle eye view" of a position, and the method I suggest is that you use the following checklist:
Each time you're on the move, look for

all the different checks available for you in the position;
all the different captures available for you in the position;
all the different checks that your opponent could make if it were their move;
all the different captures that your opponent could make if it were their move.

The reason for looking at these moves is that checks and captures are very forcing, and it will help you both see your own possibilities of scoring some easy points and it will also help you to find out what your opponent is threatening to do.
In the beginning this checklist will require some serious effort to complete for each move, but as you play more it will become easier to see the things mentioned in the checklist automatically without having to make a conscious effort.

Nice tips to be followed.

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text:
Is there a balanced chess system where players of unknown skill can have an equal chance of winning?
Is there a chess system where you can make players of differing skill levels compete against each other with an equal chance to win without using different chess variations?
This system should give good players and bad players a level playing field where both of them can win.

Yes.
The way I've done this in the past is to play a series of games with clocks starting with 10 minutes each on the clocks and then the rule for subsequent games that the winner of the previous game gets one minute less and the loser one minute more. This quickly stabilizes at a level where both players have good chances of winning.

A common way to have a large number of weak players have a chance at beating a single strong player is simultaneous chess:

image taken from http://www.chesshistory.com/winter/winter89.html
The strong player plays multiple simultaneous chess games against each of the weak players, walking from board to board. That means the attention and time of the strong player is divided among all the games while the weak players can focus their full concentration on just their own game.
The handicap of the strong player can be adjusted by adding or removing opponents.

...players of unknown skill can have an equal chance of winning...

This sounds like you want to take the player's skill out of the game which goes against the spirit and rules of chess, I would say. You could introduce elements that equalize skill differences but you may end up with a completely different kind of game, which you wanted to avoid.
For example you could introduce some kind of handicap or bonus (less time for the higher skilled, less chess pieces to begin with for the higher skilled, more chess pieces for the lower skilled (analogously to Go), other side tasks for the higher skilled) but that would require that you know the skill differences in advance or detect them while playing.
Please note, that winning chess for a lower skilled player because the higher skilled opponent had some kind of handicap is not the same as winning under otherwise equal conditions. In chess as most people play it, the definition of winning (in a statistical sense) means that you are higher skilled. Your definition of winning seems to be different (independent of skill). It would be a different kind of winning.
Indeed one could switch sides at random times as RemcoGerlich pointed out, and it would formally solve your problem, but in that case winning would be very much meaningless.
That's why I conclude that no, there is no such way. Either the stronger skilled players will win more often in chess, or the definition of winning becomes meaningless and some other kind of metric depending on the skill (like the handicap) emerges or it's simply not chess any more.

@supercat The Elo ranking system is also as quantitative as one can get.

@Trilarion: That requires having a pool of players with a wide variety of skill levels, does it not?

The ultimate handicap is teaching.
Typically we assume that the person with the winning position on the board is a winner, and the person with the losing position on the board is the loser.  But this does not always have to be true.  The more advanced player can always choose a different win condition.  Why not? It's only a game.  If the more advanced player chooses a win condition that isn't in direct opposition to the less advanced player winning, then you can actually reach a win-win situation.
You might be able to develop a clever handicap system where players have to "play their best" to beat the opponent with a specified handicap.  Go actually has this, though one quickly progresses to the point where a 2 stone handicap is too much.  If you do this, you quickly create a game of "you vs. nature"  The game becomes a zero-sum game and it really changes how it feels.
However, if your goal is to create situations to help teach the newer player, it doesn't matter how skilled you are.  You are no longer playing on the board.  You are playing in the mind.  And, honestly, we can all use a little practice in our quest to become a grandmaster at that.


text:
Blitz games managment
Here is the problem : when I have the time, i usually find the right move.
Meaning, in a longer time frame games (more than 10min) I'm doing better.
I feel like struggling with 5 min. games and I don't know how to improve.
I review my games usually using the computer but I haven't seen a big improvement, just a very small one.
To me it feels like I'm missing something that would elevate my level.
Any suggestions will be welcomed.
Thank you.

It would be very difficult, if not impossible, to help you without seeing the games. Please share a link for the games you have previously played so that we can highlight your weaknesses. Otherwise, you are likely to get general tips for blitz games.

I have an account in Chess.com witht he same nickname Quizhead.
I Can't link them all as there are dozens of them.

Tactics play the most important part of winning blitz games. The tactical player has a better chance of winning a blitz game rather than a quiet, positional player (it is the other way round for classical chess). Next is intuition. To succeed as a blitz player, you must be able to figure out the next move without going into deep calculations (i.e. 'feel' the next move). For example, here is a game from your Chess.com account I analysed with a computer:
[FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
[Event "Live Chess"]
[Site "Chess.com"]
[Date "2018.12.09"]
[Round "-"]
[White "quizhead (1238)"]
[Black "redhatkillers (1208)"]
[Result "0-1"]
[WhiteElo "?"]
[BlackElo "?"]
[Variant "Standard"]
[TimeControl "-"]
[ECO "A02"]
[Opening "Bird Opening"]

1. f4 g6 2. Nf3 Bg7 3. e4 e6 4. Be2 a6 5. d4 b5 6. O-O Ne7 7. c3 f5 8. e5 Bb7 9. Be3 Bh6 10. Nbd2 Nd5 11. Bf2 Bxf4 12. Bh4 Qc8 13. Bf2 Be3 14. Kh1 Bxf2 15. Rxf2 Qd8 16. Qc2 g5 17. Raf1 g4 18. Ne1 Ne3 19. Qd3 Nxf1 20. Bxf1 Qh4 21. Qe3 Nc6 22. Nd3 Na5 23. Nf4 Rg8 24. b4 Nc4 25. Nxc4 bxc4 26. Qg3 Qxg3 27. hxg3 h6 28. Bxc4 c6 29. Bb3 a5 30. a3 axb4 31. axb4 Ba6 32. c4 Ke7 33. Rf1 Rg5 34. Rd1 Rh8 35. d5 h5 36. dxc6 dxc6 37. Nd3 h4 38. Nc5 hxg3+ 39. Kg1 Bc8 40. b5 cxb5 41. cxb5 Rgh5 { Black wins. } 0-1

10. Nbd2 is a normal move in an opening, but unfortunately not here. Your opponent has the massive d5 square for their knight. You should have paid attention to Nd5. It forks the bishop and the pawn, and you are forced to give up the pawn. 10. g3 would've saved the pawn, though that knight is still annoying.
17. Raf1 allows a fork too. From the d5 square the knight is a serious threat. Usually when a knight is about to enter your territory, you must give it adequate attention.
25. Nxc4 looks like it wins a pawm worsens your position. Your opponent didn't notice that 25... g3 wins your rook, and fortunately you had a chance to correct that by playing Qg3.
These are just some remarks. There is still much to learn, by playing more and more games and highlighting the positions where you blunder such tactics. It happens to us all. As it is said, the player to make the next to last mistake usually wins. We all do fall for such tactics, but one needs to minimize this to have a good chance at blitz.

Thank you for your answer.
I will add to my question : After the game I can see the mistakes clearly. I want to avoid them during the game.

You cannot avoid all mistakes, but only the most obvious ones. Nothing other than training and intuition can accomplish this in a blitz game.

" 10. f3 would've saved the pawn" - Didnt you mean g3 ?

Also, G3 is a bit risky ,the knight on f3 can easily pinned and captured without the pawn who protects him

@Isac yes I meant g3, sorry.


text:
Is my representation of the Pirc Defense correct?
I tried to represents all the main lines of the Pirc Defense to play at a 2000 ELO level. Am I right with the following tree?
What I mean by right is I wonder if I do not miss any popular line or choose a bad move at some level.

Just out of curiosity, how is this tree structured? Are the branches structured in a systematic way, like in order of popularity?

Yes, exactly. Left is always more popular than right.

Ok then. I'm not sure what the tree is going to be used for, but depending on what you need it for you might need to expand/prune certain branches; for instance, the left-most leaves are the most important variations to know about in the opening and they should be expanded, while the branch 1.e4 d6 2.d4 e6 could be pruned somewhat.

Using popularity to adapt depth is really a great idea.

If you are aiming to use this tree for practical use at 2000 level, you should start in the Pirc tabiya position after 1.e4 d6 2.d4 Nf6 3.Nc3 g6. That's where it all starts, with main choices being 4.f4, 4.Be2, 4.Be3, 4.Nf3, 4.f3. (edit: Also 4.Bg5, 4.Bc4 and even 4.Bf4 as pointed in comments. And also 4.g3 and 4.h3)
That way, you will not be confused by games without ...g6 at all, like the Philidor 3...e5 or some moderns with 3...c6, 4...Qa5.
I don't think the 1.e4 d6 2.d4 e6?! branch will ever be useful to you. With Black, you won't ever want to play this. With White, if you face it you can tackle it by following general rules, and in any case a tree is not useful there. Also, I wonder how this very obscure sideline appeared in your tree. If you use popularity to select lines, have you consider how far 2...e6 lies behind 2...Nf6 ? Have you restricted your base to tournament play, if possible above a certain level (say, 1800) ?
If need be, you can build a separate tree for early deviations, like 2.Nf3, 2.Nc3 or 2.f4 - keeping in mind that they will often transpose later in your main tree in case of d2-d4. But if you have practical purposes, you want to get rid of parasitic information. That will also allow you to go deeper that move 5 - which is mandatory at 2000 level !

4 Bg5 and 4 Bc4 are also important, and I've had a number of games recently go 1 d4 Nf6 2 Bf4 g6 3 Nc3 d6 4 e4 - apparently this is a Simon Williams recommendation

After ...g6, playing Be2 and h4 with white is a popular option which is missing in your tree

There are multiple g6 in the tree.


text:
Rook and bishop vs. opposite color bishop
I drew a game with rook and bishop vs an opposite color bishop due to the 50-move rule.
[FEN "4b3/k1B5/8/2K5/8/8/R7/8 w - - 0 1"]

Is this a theoretical draw? If not, what is the technique to win?

Definitely not a theoretical draw, this should be easily winning for White. The strategy to win would be:

Advance with your king and rook to push back Black's king. If Black's light-squared bishop blocks your rook's check, then this means the Black king is on a dark square. Thus, you can use your dark-squared bishop to check the king and push it back.
Eventually you'll have pushed Black's king to either a light-squared or dark-squared corner.

If it's in a light-squared corner like a8, the light-squared bishop isn't able to act as a blockader from your rook. In the diagram you posted, here's one example of how to win:  1...Kb7 2.Bb6 Bh5 3.Ra7+ Kb8 4.Kd6 Bf3 5.Rc7 Bg2 6.Ba7+ Ka8 7.Kc5 Bf3 8.Kb6. Now all you need to do is maneuver your rook to the 8th rank to checkmate, which can be accomplished in as little as 2 moves.
If it's in a dark-squared corner like h8: Put your king on h6 and move your rook to the 8th rank, checking the Black king. If Black manages to block the check with ...Bg8, then you can checkmate immediately by moving your bishop onto the a1-h8 diagonal.

I don't know about the technique beyond trying to keep all your pieces on the dark squares and the enemy king cornered, but the position above is not a draw. According to the endgame tablebase it's mate in 10 moves. Here's one line:
[FEN "4b3/k1B5/8/2K5/8/8/R7/8 b - - 0 1"]

1... Kb7 2. Ba5 Bg6 3. Rb2+ Ka7 4. Rb6 Bc2 5. Kd6
Bd1 6. Kc7 Bc2 7. Bc3 Be4 8. Bd4 Bb7 9. Rd6+
Ka8 10. Rd8+ Bc8 11. Rxc8#

If you want statistics more generally, see http://www.maths.usyd.edu.au/u/thiel/misc/endgames/ . According to the table, for KRB vs KB, with white to move, 98.2% of positions are won by white and 1.8% are drawn; with black to move, 31.1% are drawn. Note that this table doesn't make the distinction between same-colored and opposite-colored bishops. The draws are probably positions where white loses the rook in the next move or two.


text:
Chess FEN winner
I'm new to Chess FEN notation and I'm making an online chess game, but I have one problem, I need to check after every new move if there is a winner and which one is a winner.
Can I extract that information from FEN notation ?

FEN (Forsyth-Edwards Notation) is a way of recording the current position on the chess board - piece positions, active colour, castling possibilities, en passant target, half move clock, full move number. The result of the game is not included.


text:
Why does white sacrifice their queen in this exercise?
I was doing this exercise on lichess, but I don't see why the best move for white is to sacrifice their queen in exchange for a knight (after Nh3+):
 [title "lichess puzzle 61517"]
 [fen "4r1k1/p1b2pp1/1pp2r2/3p2np/1P1P2q1/P3P1P1/2R1NPQP/2R2NK1 b - - 1 28"]

Because white will lose the queen anyway after Nh3+, since otherwise Kh1 is answered with Rxf2 trapping and winning the queen. Just try to work out the tactics by yourself.
As to why white doesn't give up the queen for the rook instead (after Rxf2), it's because in this position the knight+queen are more apt at coordinating and creating threats. For example, to see that even after Qxf2 black can win back the rook if desired, here's a line:
 [title "lichess puzzle 61517"]
 [fen "4r1k1/p1b2pp1/1pp2r2/3p2np/1P1P2q1/P3P1P1/2R1NPQP/2R2NK1 b - - 1 28"]

 1...Nh3+ 2.Kh1 Rxf2 3.Qxf2 Nxf2+ 4.Kg2 Nd3 5.Ra1 Qe4+ 6.Kg1 Ne1 7.Rxe1 Qxc2

One must bear in mind that these are tactics problems, and in this case we know white is lost anyhow after Nh3+ but you should solve them with the mindset that you're playing against an engine, that is, assume the best resistance that exists, and sometimes since the position is lost, the best resistance is to delay the unavoidable exactly similar to how engines would go about such lost positions. Therefore, Qxh3 is presumably the move that yields the best resistance (lowest evaluation value for black's advantage from the engine's pov).

Assuming that White has some reason to keep playing after losing the queen (maybe Black is almost out of time?) why is 3.Qxf2 (helping Black get his knight out of the corner) better than say 3.Nc3 Rxg2 4.Kxg2?

@bof indeed under those circumstances it might be better for white to use the tempo for a somewhat "developing" move and wait for Rxg2, however, from an objective point of view these lines will all look similarly losing. In fact if white has chances to win by flagging, then I reckon Qxh3 might give the best chances - getting rid of the pesky knight and mustering a tricky defense around the king with the two knights.

1...Nh3+ 2.Kh1 Rxf2 and White's queen is dead anyway. Sure maybe it takes a rook instead of a knight but it's non-trivial which is worth more in this position.
In either case White's king should be bringing out the white flag.


text:
When exactly does a checkmate or stalemate take effect?
I'm not enthusiastic about chess in particular, so if I use terminology incorrectly please correct me. I use "phase 1 & phase 2" for each player's move, and "turn n" for each pair of phases.
I'm a novice programmer writing a chess program as a personal challenge, and  would like to know exactly when checkmates and stalemates take effect.
Specifically:

If a player 1's move causes checkmate or stalemate, does the game end during phase 1, or at the beginning of phase 2?

Edit:
It seems I wasn't clear enough that I wasn't looking for a programming answer, I wanted to know about chess standards. Even if my program can work without detecting the exact final phase, I would like that information to be available.
I looked at the FIDE rules as mentioned in Laska
's answer [link], and Section 5 points out what I was looking for:

5.1 a. The game is won by the player who has checkmated his opponent’s king. This immediately ends the game, provided that the move producing the checkmate
position was a legal move.
5.2 a. The game is drawn when the player to move has no legal move and his king is not in check. The game is said to end in ‘stalemate’. This immediately ends the game, provided that the move producing the stalemate position was legal.

From these rules I gather that if I cause a checkmate, the game ends before my opponent's next phase, and if I cause a stalemate, the game ends during my opponent's next phase.
Please correct me if you think I'm not understanding something correctly. Also, I know I've seen the term FIDE before but I'm not sure if their chess laws would generally be considered a widely accepted and robust standard. I figure a chess community is the right place to ask about whether or not I should be using their standards.

The quoted checkmate and stalemate rules both use the phrase: "immediately ends the game." You might want to expand your question to indicate why they might be treated differently.

Take your pick.
Conventionally in computer chess, we express your idea of phases as "plies", or half-moves, where 2 plies is one "turn".
You can detect checkmate in the ply where the checkmating move is made, but it is more common for checkmate to be detected in the following ply, where your program generates legal moves for the mated player, only to find that there are 0 available.
It is often more convenient and efficient that way, as the work to generate moves would have been done anyway had the position not been mate, so no extra work is done to determine whether a position is checkmate.

Thanks for the question.
The FIDE rules are not great here. A turn ends when a game-ending move has been played (Article 6.2.a.1). The clock does not need to be pressed. But in order to compute whether the move ends the game, there has to have been some kind of hypothetical look-ahead as to what would happen at the beginning of the next turn. The simple purpose of this I suppose is to avoid the chance to lose on time after just having e.g. played a mating move.
A particular question is who has the move in the final position? In cases of mate it’s sort of obvious but in cases of stalemate it is not clear at all. Is this showing the position in the actual time or
the position in the hypothetical look-ahead? Argh!
However from a programming point of view this hypothecating is not necessary. The move is completed, and the opponent loses or is stalemated etc in their own turn. The final position cleanly shows who has the move.

Nobody has the move, as the game is over. But if it weren't, it'd be the opponent who has the move, after all the checkmating move has been made, and that means the other side has the move. What happens to the clock is relatively unimportant.

Hi @RemcoGerlich thanks for the thoughtful response. I had wondered about whether the game ending annihilates the information about who has the move. But if I can no longer tell who has the move following a stalemate then I probably can't confirm that the game is actually over! We've erased some rather necessary information. So this kind of amnesia can't occur after stalemate, and by analogy won't occur after checkmate. And hence I agree with your second point that its the checkmated (or stalemated) player who has the move in the final position.

Checkmate and stalemate end the game immediately, as soon as the move is played (that is, when the hand lets go of the piece -- but that's not relevant for computers).
If that move was White's, then that move was the last move of the game. Black never gets their turn, so in your terms "phase 2" of that turn doesn't exist.

From these rules I gather that if I cause a checkmate, the game ends
  before my opponent's next phase, and if I cause a stalemate, the game
  ends during my opponent's next phase.

Your understanding is wrong. Both checkmate and stalemate take effect immediately the move has been made. The move is made immediately the player's hand loses contact with the piece. It happens even before the player presses the clock. Hence even if the player's flag falls the checkmate or stalemate still stands.
In your terminology both cause the game to end before the opponent's next phase.

Also, I know I've seen the term FIDE before but I'm not sure if their
  chess laws would generally be considered a widely accepted and robust
  standard

FIDE is the international chess federation. It stands for "Federation International des Echecs" and is French for "International Chess Federation". It is the chess equivalent of FIFA in the world of soccer. If you understand that the FIFA rules of soccer govern the play of soccer throughout the world then you will also understand that the FIDE Laws of Chess govern the play of chess throughout the world.
Individual chess federations (governing bodies of national chess federations) may vary some rules in special cases but when they do so the tournaments affected can not be internationally rated. They can only be nationally rated.
The most common variation that I am aware of is that for competitions for weak/young players the rule which says that two illegal moves loses the game is suspended because these players play many illegal moves without thinking.

lol why is this downvoted? this answer goes even further to explain that the clock doesn't need to be pressed

There is no reason not to exit the loops your program uses after a checkmate or a stalemate. The rules of the game says there is no move for the opponent. The game is finished.
You should just break your looping and send an alert with the result and update the statics of your program.
There is not any .pgn or FEN more notation to write so no sense to still use code to perform your program.


text:
Scotch 4 Knights with 4... d5
[FEN "r1bqkb1r/ppp2ppp/2n2n2/3pp3/3PP3/2N2N2/PPP2PPP/R1BQKB1R w KQkq - 4 5"]

If Black "mirrors" White's move 4. d4 in the Scotch 4 Knights, and White wants to play sharp, aggressive moves, what would be the best move? I know that chess engines like Atockfish, GNU Chess etc. would calculate the next move forWhite as Bb5, but I want to exchange pieces. So what would the strongest capture be here?

Why do you want to exchange pieces? As white, you are pushing for an advantage. Usually, an even trade of pieces doesn't improve your position, so any simplification is just making your job of "winning this game" harder.

If you really want to capture, just turn on stockfish and see which capture is ranked highest. But in general you should be playing the best moves, and not playing according to your personal tastes in all positions.

According to 365chess.com's opening explorer, 5. exd5 is the best capture, with an 83.3% win rate.

4...d5 is really bad, if nothing else it leads to at least a clear pawn up for white in various lines that can ensue and they all involve frequent trades as well (as you desired), here are a few options starting from Nxe5 (a choice well in line with your preferences) leaning on more aggression/direct play and less positional compared to some of the other choices (like your suggested move):
 [fen "r1bqkb1r/ppp2ppp/2n2n2/3pp3/3PP3/2N2N2/PPP2PPP/R1BQKB1R w KQkq - 0 5"]
 [title "5. Nxe5"]

 5. Nxe5 Nxe4 (5... dxe4 6. Bb5 Bd7 7. Nxd7 Qxd7 8. d5 a6 9. dxc6 Qxd1+ 10. Kxd1 O-O-O+ 11. Ke2 axb5 12. cxb7+ Kxb7 13. Nxb5) 6. Qh5 Be6 (6... Nxe5 7. Qxe5+ Be6 8. Nxe4 dxe4 9. Qxe4) 7. Bb5 Nxc3 8. bxc3 g6 9. Nxg6 fxg6 10. Qe5 Rg8 11. Qxe6+ Qe7 12. Qxe7+ Bxe7 13. O-O

Note: Bear in mind that by intentionally opting for lines such as above where you favour trades and direct aggression, you'd be naturally walking into highly tactical positions, so be prepared to calculate many many relevant lines at each point (specially in the given examples above).


text:
Why might this supervised engine make mistakes based on an example game?
I am developing in my free time a python-based supervised chess engine. It is trained on past games to detect who wins (only games without draw), then it proceeds as follows:
1) find the top 4 moves based on static evaluation
2) search until depth four with minimax-algorithm
3) evaluation = 1/2 *( probability of white winning the
game + probability based on the material difference)
The first probability is based on supervised learning.
I play occasionally chess and when I played on Xboard against this engine, then me and the engine make mistakes. I wanted to ask you, based on your experience if you could look at one game (me=white, engine = black) and maybe find some explanation for the mistakes the engine makes or even maybe suggest an approximate elo of the engine, if this is possible with only one game?
Thanks for your help.(I am not sure how to correctly tag this question)
[fen ""]
1. d4 Nc6 2. Nf3 e6 3. e4 Nf6 4. Nc3 Bb4 5. Bb5 Nxe4 6. Qd3 Nxc3 7. bxc3 Bd6 8. Bxc6 dxc6 9. O-O f5 10. Bg5 Be7 11. h4 Qd6 12. Bxe7 Kxe7 13. Ng5 h6 14. Nf3 Bd7 15. c4 c5 16. Rab1 Bc6 17. Ne5 cxd4 18. Ng6+ Kf7 19. Nxh8+ Rxh8 20. Rb4 Be4 21. Qa3 a5 22. Qxa5 b6 23. Qa3 Ra8 24. Qb3 Bxc2 25. Qb2 Be4 26. c5 Qxc5 27. Rb5 Qc4 28. Qb3 Qxb3 29. axb3 Ke7 30. Rc1 c6 31. Rxb6 f4 32. f3 Bd5 33. Rb7+ Kf8 34. b4 Kg8 35. Rd1 c5 36. Rc7 Bb3 37. Rd2 Ra1+ 38. Kh2 cxb4 39. Rxd4 Bd5 40. Rxb4 Bxf3 41. gxf3 Ra2+ 42. Kh3 Rd2 43. Rc8+ Kh7 44. Rbc4 Kg6 45. Rxf4 e5 46. Re4 Kf6 47. Re8 Rd4 48. R4xe5 Kg6 49. R5e6+ Kh7 50. R6e7 Kg6 51. Rg8 Kf5 52. Rexg7 Ke5 53. Rh7 Rd2 54. Rxh6 Kf4 55. Rf8+ Ke3 56. Re6+ Kd4 57. Rd8+ Kc3 58. Rc8+ Kb3 59. Rb6+ Ka3 60. Ra8# *

Welcome on Chess.CE. Can you explain how you built your engine's static evaluation of moves ?

@Evargalo : First I build from a position a feature vector with features such as the number of attacks or attackers and the number of pieces of a given color etc. Then I train the engine to detect based on these features who will win the game (which it detects with probability 70%) Then I apply the softmax function to evaluat whites winning probability.

Well done for your engine. I think a positional mistake was 9...f5. It weakened the king position, and without any compensation in return. The move also seriously made the e5 square weak.
Why your engine didn't make a simpler 9...h6? Probably, your engine put too much focus onto material differences into your NN network? You'll have to spend some time on debugging. Your engine needed better understanding of king's safety. Your search depth was also too low.
I estimate FIDE 1600 for your engine.


text:
A master-level game in which one player did not move beyond the third or fourth rank?
Has there been a game of master level or above in which one player did not move any piece or pawn beyond the third or fourth rank?

Plenty of shortish draws would qualify. For instance there is a well known three-fold repition in the Najdorf where white does not move beyond the fourth rank: https://chess.stackexchange.com/questions/15860/najdorf-threefold-repition Also it is a relatively popular line with grandmasters who are satisfied with a draw as white.

Because of this I think you need to qualify your question, by either limiting it to the 3rd/6th rank (probably very few if any high level games or by specifying a minimum number of moves for the game or perhaps by excluding draws.

Many quick "grandmaster draws" have proceeded along these lines.

Thanks for your question and welcome to chess.stackexchange :-) This is the kind of question which Tim Krabbe would have answered fascinatingly!
I choose to focus on the question where both players didn’t move beyond the fourth rank. There must be thousands of games where one player kept back.
Early games from the “romantic” period which featured open openings and aggressive sacrifices were the norm until the end of the 19th century. So don’t expect anything from that time.
Later, the revolution led by Reti and Nimzowitch led to much more positional play with indirect control of the centre from a distance. However, it seems unlikely to be able to win such a game, without moving forwards.
If neither player moved beyond the 4th rank, then no captures have taken place. So it’s hard to see what kind of winning advantage one side could have accrued. There must be many agreed draws, but they don’t really count. I would be very interested to see what a won game would look like with this constraint, as I can’t imagine it.


text:
Can one improve their chess without playing online?
I have been playing chess for almost a year and I'm addicted to playing chess on Lichess.
My stats there are:

2100 classical
2000 rapid
1800 blitz

I feel that playing chess online ruins my life and that my life would be much better without it at the moment.

I'm studying at University and my grades have dropped.

I'm not devoting enough time to my work place.

I'm barely going out with my friends

I do less sports

I've dropped some of my other fun hobbies

I sleep very late

I barely go on dates

All of these are results of my online chess addiction.
However, after all that said, it makes me sad to think that I will give up chess completely. I still want to keep my playing skills and improve.
Can a chess player keep himself in shape by only studying chess (which is not as addictive as playing online) and playing long time control OTB tournaments once in a while? Or should I quit chess completely?
Please help me by finding some things that I could do to stay good at chess while not playing online.
Edit:
I'm mainly addicted to blitz, the problem is that I lack self control to restrain myself from playing it. I have tried a few times to stop playing only blitz but failed to accomplish that and went back to my bad habits. I wish there was an option to open an account that would only be allowed to play long time control games, to help people like me. Once I play blitz I usually just crave reaching a specific rating and I play like am possessed.
I started playing in a local chess club a few months ago. I already got to play 3 long time control tournaments, quite successfully, and I want to keep my level there. I fear that without this abusive online playing my abilities OTB will be damaged.

I'd like to start with this comment of yours:

"I fear that without this abusive online playing my abilities OTB will be damaged."

I know where you are coming from, because I've been there, too. I used to be ridiculously addicted to chess - and I wasn't even very good lol. Now it's a hobby, which is much more healthy.
I also know that fear you speak of - I, and people like myself (which presumably includes you) strive for depth, rather than breadth in life. Being very good at one thing seems so much more important than being kind of good at a lot of things; trouble is, I picked the wrong thing.
Personally, I had to completely stop playing chess for a while. When I came back to it (in a more recreational fashion), I was indeed worse at chess, and though I have improved, I'm still not completely back to where I was (although I strongly suspect I'll get there).
It was completely worth it.
I had free-time. I had sleep. I had better grades. By golly, I even had more friends - not fair-weather friends, but honest-to-goodness friends that cared about me and my life.
I say all of this to encourage you that even if your playing ability drops off, please don't worry about it. Chess is not your life. Your life is your life. Go out and live it! Study with all of your strength, go on dates, hang out with your friends, work your rear end off and become the absolutely amazing, incredible person that you are - one that's always up for a relaxing game of chess with a friend, of course.

Now for the practical suggestions:

Here are some suggestions for maintaining playing strength while limiting online chess:

Study master games. Seriously, doing this will get you way more chess knowledge than playing oodles of blitz games.

Read some chess books, playing out the games on the board if you wish. These books are almost always entertaining as well as being extremely helpful.

Play casually OTB with some friends, analyzing various lines at a relaxed pace - chat with a friend (or maybe even a date) over a nice, no-pressure, slow game (although if it's a date, make sure that she likes chess first XD).

Visit you local chess club, and play some games there when you're in a good spot with your schoolwork and workplace work.

TL;DR: it really is possible to enjoy chess and have a life.

I agree with itub's comment. You don't neccessarily have to give up on playing online altogether, but ask yourself whether you just play on at times, game after game, like you're possessed.
Does chess become an obsession rather than recreation? Does this happen to you for all time controls?
In general, obsessive playing is more likely when playing blitz (or even faster time controls than that) due to prolonged adrenaline rushes being more likely in faster time controls (in general you get some time to calm yourself down between moves during a longer game).
If you feel like the situation is getting out of hand you shouldn't hesitate to take a break from online chess for a while, and remember that taking a break for now doesn't mean you have to give up playing for the rest of your life. Another thing that you could do that itub also suggested in his comment is to join a local chess club and play chess OTB in general. One of the issues with online chess that makes it addictive is that there's always someone willing to play you online, no matter what time it is, an issue which doesn't really exist with OTB chess in general.
When it comes to keeping oneself in shape chess-wise, I think you don't need to worry that much. If you stop playing completely you will naturally get rusty, but your ability to play will not disappear very easily. When I was inactive for a while during my years as an undergrad I had some issues when I started playing again, but these issues were intimately connected with time management and self-doubt, and after a tournament or two I was already back at full strenght. In general, if you play about 4-5 OTB tournaments a year I have a hard time seeing you even getting rusty in the first place, and if you work on your chess inbetween tournaments by studying chess in general I don't see why you couldn't improve.

In my opinion, online chess often does more to ruin your game than to actually improve it, as most of the time we are just playing Blitz, with not too much thought and with zero analysis of the game
So review your games (I mean, actually do it, not just run them through an engine), find your weakest point and get your hands on a good chess book that treats that topic in depth. A coach is not a bad idea if you can afford it either, but even if you can't, it won't be hard to find some "chess pals" and train with them.
Finally, on the matter of self-control: 1) Try harder! 2) Avoid the temptation by not logging into the site at all! When you play blitz, let it at least be a social activity at the chess club/bar/whatever you're closest to

I would recommend playing in tournaments at your local chess club.  Aim for longer games with at least 30 minutes for each side (the longer the better).  Based on your online rating, you should be somewhere in the middle of the field depending on the strength of your club.
It may take you some time to adjust to playing over the board if you aren't used to it.  However, with practice your online chess skills should transfer to a physical chess board just fine.

If chess is stopping your normal life you should just stop it. It’s not a career for you.
Fischer played better chess than you but never played online. It’s of course possible to improve without playing online. Why not read digital books like Chessable.com? What about study your own game with a computer?
Come out for real tournaments to gain FIDE points whenever you have some time.

Chess is addictive.
Yes you can improve more by not playing online.
But your LIFE would improve even more than your chess if you gave it up or at least made it a very casual hobby instead of trying to improve your game more.  You will NOT be a GM.  I guarantee it.  And if you did, they are a dime a dozen these days.  So if you are not in the handful of top world players you will not make any money at chess.
WHY are you playing chess at all?  Your list pretty much says chess is messing up your REAL LIFE.  If you are logical enough to play chess well you are logical enough to know you should stop playing.
Now, chess is addictive, so find some professional help to break that addiction.
@user19048

Play against Computers instead of humans. I found that playing against the computer is less addictive, as there is no ego involved.
There is a new artificial intelligence called Maia who plays like a human. You can play against it.
Keep solving puzzles daily to keep yourself tactically fit.

I'm not a psychologist, but I think you should find out if you are an addiction-prone personality. If yes, then chess would be one of the better choices, since you just might land at another addiction to get the kicks. Willpower is the magic word, and as a chessplayer, your chances are good anyway.
To answer the direct question, I never played online chess in my life and never will do, and still I'm quite strong. It will be an interesting experiment to find out what happened to my ELO after the pandemy, but I guess a few tournaments will put me into shape again. So I don't think it will ruin your ELO giving up online blitz if you read some chess books, solve tactics etc.


text:
An objective measure of the difference in strength between top programs and top human players in the four most popular forms of chess?
Is there an objective measure of the superiority (or otherwise) that the strongest computer programs enjoy over the strongest human players which can be compared across the four main forms of chess, namely western chess, xiang qi (Chinese chess), shogi (Japanese chess), and makruk (Thai chess)? For example, can it be said that on comparable Elo scales the programs have say an x point advantage in western chess, a y point one in Chinese chess, and lag behind in the other two games by z points?

Western chess is from India, so it's the Western-most chess after all. Nice definition!

I would have to answer no in my opinion. The four forms of chess are different. Shogi from what I remember is a form of chess where capturing an opponent's piece allows you to, at a time of your choosing, put one of that piece on the board as yours. Now that is a level of tactical complexity that surely gives any engine a huge advantage over any strength of human. I have played a little Xiang Qi and I would say the same; in the 90's when Chinese players played Professional western chess for the first time they were awesome tacticians; Xiang Qi as their previous game being very tactical led to that.

While it is possible to write engines that can play different chess-family games, doing so generally yields an engine that are only "competent" at each one, at best.  The best engines for each individual game incorporate specific knowledge and optimisations for that game, and are usually incapable of playing the others.
Many standard chess engines are not even capable of playing Chess960 correctly, because there are special rules for castling due to the variety of starting positions, even though the rest of the game is identical.  However, adding this capability does not usually weaken the engine in the way that adding support for Shogi would.
Shogi, in particular, is very difficult to adapt a standard chess-playing engine to play well - even "fairy chess" engines which can support Xiangqi relatively easily.  The immediate stumbling block is generally the piece-dropping mechanic, which completely explodes the branching factor of the game tree - so it is very difficult for an engine to explore the game tree to sufficient depth to treat the game in the tactical manner that engines usually do best at.  Instead, Shogi has to be treated as a positional game, requiring a sophisticated positional analysis function to determine the correct lines to explore.  Human players are naturally better at acquiring this knowledge than computers.
Conversely, a good Shogi engine would need to be taught about the special en passant and castling moves in standard chess, which don't exist in any form in Shogi, as well as the way pawns capture differently from moving, and the way in which pawns can promote to several different pieces rather than just one.  All of the specialised Shogi positional knowledge that made it a good Shogi engine would then be useless for playing standard chess.
So the correct approach is to measure any given player's or engine's strength on an individual game.  This will generally not be correlated strongly with its strength on a different game, if it is even capable of playing it.


text:
Why is 5. f5 so necessary in the Dzindzi-Indian Opening/Modern Defense: Pterodactyl, Beefeater Variation?
I have played a couple of games as black with this line. It is a simple plan: to put pressure on the weak c3 and c4 pawns.
This line is mainly known as the Dzindzi-Indian Opening, according to the comments and this video. It's also called the Modern Defense: Pterodactyl, Beefeater Variation according to chess.com.
[FEN ""]

1. d4 g6 2. c4 Bg7 3. Nc3 c5 4. d5 Bxc3 5. bxc3 f5

I have tried it while playing correspondence, so I have followed the move suggested by databases: 5. f5. This has had good results after quickly playing Qa5, trying to attack the weak pawns along with other minor pieces.
5...f5  347
2018    2403/2426/2709   30.3%  25.6%   44.1%
5...Qa5 22
2017    2359/2306/2586   50%    22.7%   27.3%
5...e5  5
2014    2370/2338/2418   40%       20%     40%
5...d6  1
2010    Steadman vs. Bosboom 0-1
*Chesstempo database for the position
I wonder what the reason is for taking away a tempo to play f5 while the plan is clear, at least as I play it: to profit from the doubled pawns by attacking on the queenside.
Is f5 played to avoid e4?

@Rewan Demontay No it is ok, same sense. Thank you for making my text more clear and btw giving me the oportunity of learning a bit of english wich I like to do.

I think the variation is named pterodactyl variant. Maybe it should be specified at the title.

@Rewan Demontay I would like to clarify I have followed the move sugested by db. I feel unfair in this cases to edit it, so please delete that s and I will do it myself too with the last comment.

@Rewan Demontay no, only after the diagram change the moves --> the move. As this is not a line very sugested on db. I do not have followed the 5 moves. I followed f5 only, while with no assistance I would have played Qa5

This line is better known as the Dzindzi-Indian Defense. You will find a lot of material under that name.

@Rewan Demontay. chess.com is a good source for the variation. It is on modern theory so that the befeeter name I guess.

@fuxia. No, at Dzindzi-indian Defense I do not see black tradding his bishop on move 4

@Rewan Demontay No I just say I have played this specific move, not the moves sugested by db so I prefer: "I have tried it while playing correspondance, so I have followed the move [s] sugested by databases. It is just to change a word

@Universal_learner Beefeater is the ECO name, but Dzindzi-Indian is the name this variation is called normally. It's the same thing. Here's an Introduction video explaining this. f5 is mandatory to make e4 a bit more expensive for White (it's still a good move).

@fuxia I saw a first video where the plan is the same but BxN is not played before f5. But you are totaly rigth this is also named Dzindzi_Indian I realized after reading some posts and watching my second video

You don't want a White pawn getting to e5, especially with a friend at f4.  White can let you have a c-pawn if he can achieve such a central dominance.
Also, without f5 it is awkward to develop the Ng8 -- you notice none of the variations you show have Nf6.  But now after f5, Nf6 will grip the e4 square.   Thus White often plays e4 anyway!

By playing ...f5 you're trying to weaken the e4 push. This is the most important immediate thing to attend to. It's not like White's doubled pawns are going to run away anytime soon.

f5 has the aim to stop the e4 push. However, a "refutation" of the line is 1. d4 g6 2. c4 Bg7 3. Nc3 c5 4. d5 Bxc3 5. bxc3 f5 6. e4 fxe4 7. f3!; Here, if black captures in f3, then white has a strong attack due to the better development. Therefore, in his DVD series on the Dzindzi, GM Ron Henley suggests 7. ...e5!, but he doesn't consider the first choice of Stockfish, which seems very good for white: 8. Nh3! with the idea of Nf2 (ff 8. ... exf3 then simply Qxf3).


text:
Winning plan for black in this line of French Defense: Advance Variation Main Line
I play the French Defense as both white and black. I often play this line with black suggested by Korchnoi if I am not wrong. I have found a way to prevent the sudden b4, via Bd7 (if 8.Rb1 Bd7 9.b4 cxb3 10.Nxb3, I can answer with 10...Ba4, pinning the queen and winning material).

[FEN "r1b1kbnr/pp3ppp/1qn1p3/2ppP3/3P4/2P2N2/PP3PPP/RNBQKB1R w KQkq - 3 6"]

6. a3 c4 7. Nbd2 Na5

The problem is, although I feel comfortable with the limitations white has in development, I do not often find a winning plan as black and I end up finishing by playing for a draw.
What are your thoughts as to what I could do here?

Your setup stops b4 but in exchange you release all the pressure you had on White's centre.

Once stuff has settled down on the queenside, you may eventually castle there and create play on the other sector, with moves such as ...f6 or ...f5 Take a look at a few illustrative games that may help you understand how to put this into practice


text:
Should an arbiter claim draw at a K+R vs K+R endgame?
I was asked for first time to help at a non federated tournament for kids to arbitrate their games, played at 30 minutes with no increment time.
It was a scholar tournament and they made mistakes as leaving checkmates in one, let the queen to be captured etc.
At one game both kids arrived to a K+R K+R endgame. There was not a way to quickly gain the rook and win the game and both kids had time.
One kid claimed it was a draw. We were two arbiters (not experts, just two 1900 helping a bit at the club).
We claimed draw.
Was it a correct decision or we should have left the kids play?

Now the question is: Why on Earth don't you give time per move?

There was no increment at the tourney @David they both have 25 minutes on his clock anyhow so I guess I should have asked the kid that had not offered draw if he wanted to play the 50 moves

Finish games are a source of trouble when players reach "zeitnot". It is also hard to keep track of the 50-move rule when players are not writing the moves. If all big tournaments have moves away from no-time-per-move games, that may be for a good reason

Yes I was wondering myself it would have been a task to count the 50 moves with no notation.

@David at blitz 5+0 I had seen at a fed tourney a player winning by time a k+n vs k+pawn. The player with the knigth didn't capture to win on time (there is mate chances with the pawn) and the arbiter in this case didn't claim draw.

And that's why you shouldn't use finish tim controls

In general a draw should be claimed if one player is in danger of running out of time on the clock. If this doesn't apply, it's best to let things go until the 50 move rule is reached. Note that I'm not going by any official FIDE rules here.

You can declare a draw and in fact you are required to declare a draw but only after you have counted 75 moves by each side without a capture or a pawn move. This is according to the FIDE Laws of Chess article 9.6.2:

9.6 If one or both of the following occur(s) then the game is drawn:
9.6.1 the same position has appeared, as in 9.2.2 at least five times.
9.6.2 any series of at least 75 moves have been made by each player without the movement of any pawn and without any capture. If the last
  move resulted in checkmate, that shall take precedence

Of course the players are also free to agree a draw between them.
EDIT: blues makes the following comment:

III.5.1 may also apply. If the arbiter agrees that the opponent cannot
  win by normal means, or that the opponent has been making no effort to
  win the game by normal means, he shall declare the game drawn.
  Otherwise he shall postpone his decision or reject the claim. This
  does not require 75 moves or fivefold repetition

I will answer that here since there is insufficient room in a comment to do so.
Guidelines III.5.1 almost certainly does not apply in this case. III.5.1 is not standalone. It is part of section III and is dependent on earlier parts of III.
Let's take a look.

Guidelines III. Games without increment including Quickplay Finishes
III.1 A ‘quickplay finish’ is the phase of a game when all the remaining moves must be completed in a finite time.
III.2.1 The Guidelines below concerning the final period of the game including Quickplay Finishes, shall only be used at an event if their
  use has been announced beforehand.
III.2.2 These Guidelines shall apply only to standard chess and rapid chess games without increment and not to blitz games.

First, according to the OP, the time control was all moves in 30 minutes, so a rapid time control and no increments mean it is possible that III applies. However according to III.2.1 these shall only be used at an event if their use has been announced beforehand. They were almost certainly not announced beforehand, else the two arbiters would have at least know of their existence and they appear not to.
Suppose they were announced beforehand. Then we come to:

III.4 If the player having the move has less than two minutes left on
  his clock, he may request that an increment extra five seconds be
  introduced for both players. This constitutes the offer of a draw. If
  the offer refused, and the arbiter agrees to the request, the clocks
  shall then be set with the extra time; the opponent shall be awarded
  two extra minutes and the game shall continue.

The OP in one of his comments seems to say that both players still had 25 minutes left. This would mean this does not apply. Nevertheless supposing the player did have less than 2 minutes left, the arbiters cannot apply this rule unless the player specifically asks for it. The arbiters are not allowed to help the players in any way and may not volunteer this information during the game. They may only make announcements informing all players before the game.
Continuing, we finally reach the part blues references:

III.5 If Article III.4 does not apply and the player having the move has less than two minutes left on his clock, he may claim a draw
  before his flag falls. He shall summon the arbiter and may stop the
  chessclock (see Article 6.12.2). He may claim on the basis that his
  opponent cannot win by normal means, and/or that his opponent has been
  making no effort to win by normal means

First, this can only apply if III.4 does not apply. The only way that can happen is if there are no digital clocks capable of being set with the required time and increment. If such clocks are available then III.4 applies and III.5 does not apply.
Suppose, however, that all the previous counterfactual "if onlys" apply then III.5 can only apply if the player also knows the rule and makes the specific request in the correct manner. Again, even if the arbiter knows the rule he may not help the player by volunteering the information.
Hence my original conclusion that - Guidelines III.5.1 almost certainly does not apply in this case.

III.5.1 may also apply. If the arbiter agrees that the opponent cannot win by normal means, or that the opponent has been making no effort to win the game by normal means, he shall declare the game drawn. Otherwise he shall postpone his decision or reject the claim. This does not require 75 moves or fivefold repetition.

IIRC there's a little controversy over the 75-move rule that popped up after some computer sims showed that certain "known draw" endgames with only a couple pieces turned out to be forced mate in 3or 4 hundred moves.

Yes they both had around 25 minutes of time with no increment.

It is not a drawn position according to the rules, since there is sufficient mating material. It may be a draw from the point of view of endgame theory, but given players who make lots of mistakes, it wouldn't be all that surprising for one to lose to a tactic.
I would let them play until the player who wanted a draw can claim it based on the 50-move rule or threefold repetition, or someone runs out of time or the game ends some other way. (Were they keeping notation? If not making a proper claim could be difficult, although an arbiter who witnesses the game could rule it a draw after 75 moves or fivefold repetition. Also note that USCF rules allow the arbiter or a deputy to count moves, if requested, for a 50-move claim under sudden death.)
That said, for a "non federated kids tournament", I suppose you may have some leeway, so I wouldn't really fault you for ruling it a draw.

No notation they played very basic after some lessons at school. Made illegal moves etc. Well we may have asked the other kid if he agreed with the draw or wanted to play 50 moves. They get a cup as first and second with 3,5 point. They looked happy with the cup so I guess we were almost correct as the second kid was loosing before he loosed his two pawns and looked happy too :) he didn't claim for continue playing and both were happy :)

You may want to refrain from mentioning that there's sufficient mating material at a kids' tournament.

It's better to let them play it out a bit and ideally only draw once reaching 50 moves. But if one of them is low on time (and their opponent is clearly just trying to flag them) then you should claim the draw.

Exactly. An arbitrated draw should mean "If I took the clock away and just had you play, I'm confident that the game would be drawn by the 50-move rule or repetition. The only thing the clock is doing is forcing one of you to lose on time." With children who are making mistakes, you can't be confident that the game would be drawn without the clock. But, hey, it sounds like it was just a for-fun tournament so no biggie.

@DavidRicherby The clock is part of the game though. If one player can force the other to lose on time, why should the arbiter step in to prevent that?

@orlp If the clock is so fundamental, why so a lack of mating material and the 50-move rule constitute draws? Shouldn't the players just keep going until one of them loses on time?

@DavidRicherby Without the 50 move rule drawn positions would end up being an exercise in dexterity rather than wit: who can move their piece the fastest and hit the clock. I do think the clock is fundamental but has that issue in ending games without additional rules.

@orlp Make your mind up. First you say "If one player can force the other to lose on time, why should the arbiter step in to prevent that?" and then you say that "drawn positions [shouldn't] end up being an exercise in dexterity rather than wit: who can move their piece the fastest and hit the clock."  Which is it?

@DavidRicherby I don't see those two being contradictory in most situations.

@orlp I don't understand how losing on time in a drawn position is anything other than losing an exercise in dexterity rather than wit, by failing to move one's pieces fast enough and hit the clock.

@DavidRicherby A theoretical drawn position does not mean that a player can achieve the draw. For all we know maybe chess itself is drawn in the starting position! It still takes thinking to achieve a theoretically known result. On top of that, if you have a time disadvantage going into the endgame that is a result of wit - not dexterity. Even if we allocate 5 seconds of 'dexterity' per move for moving a piece and hitting the clock you still won't run out of time with a mere 5 minutes left on the clock to hit the 50 move rule.

@orlp It depends how trivially simply the theoretically drawn position is. Something like a Dvoretsky exercise is obviously not subject to a draw claim, but Rook vs Rook is trivially simple.

It is difficult to say what the exact rules should be if you aren't affiliated with a group that publishes rules for such situations. But I think your actions in this case were reasonable.
USCF rule 14H used to state that a player with less than two minutes on the clock (with no delay or increment being used) could make a claim of insufficient losing chances. Officially, that rule is no longer in effect, although a tournament is still allowed to use it as a variation without announcing it in advance.
If this variation is used, then rule 14I4 specifically states that rook vs rook should be a draw unless it is a position where there is a quick win. In general, if a class C player with ample time would not reasonably lose the position against a master, then the draw claim would be upheld, under this variation. This is regardless of the actual strengths of the players involved or how little time is on the clock.
Since there were more than 2 minutes on the clock ("both kids had time") technically this variation could not have been invoked. However, an attempted draw claim also constitutes a draw offer, which the other player may accept even if the claim is not upheld. According to your comment on another answer, you asked the other player if they agreed with the draw, and they seemed happy with it. That would be good enough for me. If neither player wanted to play on, there would be little point in forcing them to shuffle the pieces around for 50 moves. It's possible that novice players would not even be aware of the possibility of simply offering a draw.
The part of the USCF Official Rules of Chess book which contains the rules is now available online, by the way. I found it here.

What about a situation where a player and her teammates want to go home at the end of an evening of play, but an opponent who refuses a draw has an hour or more on the clock or would reach the next time increment before the 50-move rule would kick in?  While the rules of chess would nominally allow the player to force everyone to either stick around for an hour more or else forfeit, I would regard an attempt to eke a win out of such circumstances as unsportsmanlike conduct.

@supercat Whether it's unsportsmanlike to play on in a drawn position is a matter of opinion - certainly novice players are capable of blundering. And it may depend upon the exact position (for example, maybe it's a drawn rook vs rook position, but the enemy king is trapped along the side, and checkmate isn't out of the question if the opponent isn't careful.) If you think that's unsportsmanlike, then you can use the 14H variation. Also, according to USCF rule 18G, the TD can adjudicate the game in an emergency. 18G1 gives the example of a player who is letting his clock simply run.

Interesting the use of the term "emergency" for that situation.  Perhaps the greater emergency would be the fact that if all other games are settled and the result of the last game would be needed to seed the next round, it would be absurd to delay all games that would be affected by the seeding.

Relevant FIDE rule, appendix G.5:

If Article G.4 [a player may claim extra time for both sides] does not apply and the player having the move has less
  than two minutes left on his clock, he may claim a draw before his
  flag falls. He shall summon the arbiter and may stop the chessclock
  (see Article 6.12 b). He may claim on the basis that his opponent
  cannot win by normal means, and/or that his opponent has been making
  no effort to win by normal means.

Similar to the USCF rule cited by D M, technically this can only be invoked if the claiming player has less then two minutes on their clock.

You are using an out of date version of the FIDE Laws of Chess. There is no Appendix G. See my answer for a link to the current laws.

@BrianTowers Ah, you are right.I should have checked for that. Interesting though. Do you know why this appendix was thrown out? Too much ambiguity/power to the arbiter?

What was in Appendix G has now moved to a new section of "Guidelines" at the very end. The "Guidelines" deal with aspects of chess which the English Chess Federation, which is still struggling to come into the 21st century, wants to retain - play without digital clocks / increments and adjournments. It also deals with chess960. FIDE reviews the laws every 4 years. The next review is in 2021 when it is planned to scrap the laws dealing with 20th century anomalies like analogue clocks and adjournments. How can you have adjournments in the age of laptops and engines? Crazy!

@BrianTowers Are adjournments with laptops and engines really that much more crazy than adjournments with your buddies, the ex-world-champions, as seen in the days when adjournments were still the norm in matches and tournaments?

@BrianTowers: Well, the rules on adjournments were designed such that both sides in the game had the same chances at trying such shenanigans.


text:
Historical origin of the queen as a chess piece
As far as I know, chess was introduced at Europe from Arabia by a Spanish king: Alfonso X.
I recently read an article in Spanish press saying the queen was also introduced as a piece in Spain.
The article says historians Govert Westerveld and Marilyn Yalom confirm it is a tribute to Queen Isabella of Castille.
I wonder if this article is biased (the title of the article affirms "The chess queen is Spanish"), as it is from my country, and there are other theories about the origin of the queen in chess than being a tribute to our known medieval queen Isabella.

Not a full answer, but a relevant article.

I have read the claim about Queen Isabella somewhere (and not in Spanish press). However, the claim about Alfonso X is clearly false, since Chess had reached Europe at least two centuries before his birth.

@Evargalo I totaly trust I have surely heard biased info as my country always try to claim an historical importance on chess (and what is no chess). I hoppe that encourages an answer!

A basic problem is to define terms and criteria.  What is needed to 'have introduced chess' in Europe? Is it enough to find chess men mentioned in donations or bequests?  Or do we need proof that the rules of the game were known?  Or perhaps even that they were used to play according to those rules?  Is an introduction that we find one mention?  Or do we need to have a significant number of people with chess pieces, or playing chess or whatever?
Murray's  A History of Chess mentions wills from the family of Counts of Barcelona, at least one of is dated to early 11th century, thus before Alphonso X. So Alphonso appears to be out as point of origin. He also notes multiple mentions of the game during the 12th century (i.e. in the 1100's), adding to the problem of having Alfonso introducing the the game, except in very limited sense. (The nordic game 'skak-tafl', which is usually taken to be chess, was played in 11th and 12th century -- which may be an added problem in connecting Alphonso X with the game.)
There are also indications that the games was known to Europeans even earlier, outside Europe.  If that is correct, it certainly opens for other vectors of transmission into Europe than through Spain.  Even though the game is more likely to be found mentioned in writing in relation to royalty, high nobility or priesthood, (as they were mainly those who left written documents) there seems to be no clear reason why tradesmen and sailors anywhere necessarily must have been ignorant of the game.
As to the name of the queen itself ... I'll leave that for others. Murray suggests that the name of the piece we call Queen was part of the Europeanization of the game: in Europe, a queen was perhaps the only generally recognized piece to have a natural place beside the king. Besides 'Queen', version of 'ferz' were also used -- there seem to be Spanish sources using the term 'alfferza' as well as connecting it to the idea of a standard-bearer.  If Spain could be shown to be the sole or main point of entry of chess into Europe, then the naming of the queen would probably originate in Spain as well.  But until that has been shown definitely, origin of terminology is probably best treated carefully.
But again, perhaps, the question of what the question really is may need to be asked.  Yalom connected the modern queen, with its added powers of movement, with Isabella, not the old queen piece.


text:
Why is Na5 not played in this line of the French Defense, Advance Variation?
I find Na5 a good resource for black in this line of the french, profiting from the fact that white's b-pawn is binned to the bishop. As far as I can understand this position with my limited chess, I find it a strong move, winning space on queenside with the plan of trying Bd7-Rc8-Nc4 on c-file.
[FEN "r1b1kbnr/pp3ppp/1qn1p3/2ppP3/3P4/2P2N2/PP3PPP/RNBQKB1R w KQkq - 3 6"]

6. a3 Nh6 7. b4 cxd4 8. cxd4 Nf5
9. Bb2 Na5

However, I don't find this move at the database of chesstempo I use to use for my correspondence games.

Stockfish neither considers it. It even don't play 10....Nbd2 (it plays Nc3) to defend on c4 (which I would expect), and doesn't wonder at all about Nc4 (it simply trades his bishop for the knight; apparently it should result an advantage on the center).
What's my misunderstanding here?

Strictly speaking, the pawn on b4 is the pinned piece  (pinned to the bishop).

@Brandon_J true. thanks for the clarification and the edition.

The plan you outlined with ...Bd7, ...Rc8, ...Nc4 is a good strategical plan, but there are a few concrete reasons it doesn't work well:

In the opening you should be focusing on developing all your pieces and castling. Your plan with maneuvering the knight to c4 will move the same piece three times.
At depth 33, Stockfish gives 10.Nc3 Bd7 11.Rb1!, breaking the pin on the b2-bishop and attacking the a5-knight. Now you have to move the knight before your a8-rook manages to reach c8. If you go ahead with 11...Nc4 then 12.Bxc4 dxc4 is poor for you. Your new pawn on c4 is mainly a weakness at the moment, and White may blast open the centre with d5 to attack your uncasted king.
Also, White could always play 10.Qa4+. If you block with 10...Bd7 then 11.Qxa5 wins the knight. So you have to respond with retreating the knight: 10...Nc6.

I suspected the rupture of the center could cause troubles and didn't realized there was Qa4

I learned that resource on the club some years ago, but I don't remember if it was on books. However the position where Na5 can be played profiting the undefeanded bishop on b2 should be sligthy different.

@Universal_learner Actually I just checked my reference DB and it turns out if you play 9...Bd7 and 10...Rc8 first, then 11...Na5 has been played a fair number of times (since you're basically two tempi ahead in your operation assuming White hasn't prepared to counter it). However, the problem is White could always play Nbd2 and then on ...Nc4 Nxc4 ...dxc4 you're still left with a pawn on c4 and White can blast open the centre with d5. In any case this might have been where you saw the idea.

The Nbd2 --> Nc4 plan to protect the bishop doesn't work because c4 is attacked by black's pawn. Stockfish takes a more direct route to kick the pin:
[fen "r1b1kb1r/pp3ppp/1q2p3/n2pPn2/1P1P4/P4N2/1B3PPP/RN1QKB1R w KQkq - 0 1"]

1. Nc3 {White can kick the pin in a moment.} (1. Nbd2 {This move also poorly develops the knight - and as you can see, c4 is covered anyway.}) 1...Bd7 2. Na4

And the pin is already gone. Na5 didn't really do anything in the first place. It was interesting while it lasted, but that wasn't long. It wasn't exactly a bad move, even (lichess would call it an "inaccuracy," I'd wager); however, there are better ideas here, such as the simple developing move Bd7.

I meant with my poor english Nbd2 to prevent blacks Nc4. However stockfish doesn't worry at all about what I suposed a little hole and if black's knigth goes to c4 it simply trades it for his f1 bishop (on the Nc3 line), not wondering neither about the passed pawn generated on c4.

@Universal_learner Yeah, Nc4 by black could end up being a liability. It would indeed produce a passed pawn, but for practical purposes, an isolated passed pawn. Besides, if black wants any chance at controlling the c-file, why put a pawn on it?, etc. Solid thinking on your part, but not Stockfish-perfect thinking - and no one can reach that, anyway, so don't feel bad.

Maybe the problem is queen's position don't allows b5 to support the passed pawn. As Nc4 isn't a choise it is a move that migth finish with loosing some tempo after knigth's return to c6

Absolutely@Universal_learner