What are the ideas behind the Blackmar-Diemer gambit? I have a new chess student who likes risky openings. We conducted an exercise where we played the first 4 or 5 moves to see which openings come naturally to him. He chose the Scandinavian Defence and Queen's Gambit Accepted as Black, and the Blackmar-Diemer gambit as White.

[FEN ""]
1. d4 d5 2. e4


My problem is that I have only come across this opening once, and it does not appear in any of the books I have. It also is that my style of play is very different from my student's. I have a much more cautious style.

So, my question is, to help my student, I would like to know what are the main ideas and variations in the Blackmar-Diemer gambit?
I've used BDG countless number of times and won virtually everytime over weaker players. This is a dangerous opening if Black simply plays normal development moves, quite tricky to play in a 5-minute blitz game.

White has to attack because he is a pawn down. The most direct and surprisingly effective setup is:


Position the light bishop on the d3-h7 diagonal
Move the white queen d1-e1-h4
Prepare for an exchange sacrifice on the f-file
Prepare for bishop sacrifices on the h6 and h7 squares


Why is this effective in a blitz game? An unprepared Black player might just simply make normal development moves, as if there was no gambit. By the time Black sees the checkmate, it'd be too late. If Black plays h7-h6 or g7-g6, White has the the two bishops and f1-rook to do further damage, for example sacrificing by Bxh6.

This gambit can be refuted, possible ideas:


Castle to the queen-side
Delay castling and strike on the weak d-pawn. If white plays c3, Black has ...c5 to challenge the pawn and try to open the weak g1-a7 diagonal.


I've personally found very difficult to deal with Black castle queen-side, because it is harder to exploit the space advantage in the king-side while the Black king is on the other side of the board.

Here, I give a sample game that I've used many times.

[FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
1.d4 d5 2.e4 dxe4 3.f3 exf3 4.Nxf3 Nf6 5.Bd3 e6 6.O-O Bd6 7.Bg5 O-O 8.Qe1 Nbd7  9.Qh4 c5 10.Ne5 cxd4 11.Bxf6 Nxf6 12.Rxf6 
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