Should I play the Cozio defense deferred? The Cozio defense to the Ruy Lopez:

[FEN ""]
1. e4 e5
2. Nf3 Nc6
3. Bb5 Nge7
4. O-O


The Cozio defense deferred:

[FEN ""]
1. e4 e5
2. Nf3 Nc6
3. Bb5 a6
4. Ba4 Nge7


The deferred variation speaks more to me because I typically play a6. From the Opening Explorer, I think the best continuation for white is d4 followed by bringing the queen out to the center:

[FEN ""]
1. e4 e5
2. Nf3 Nc6
3. Bb5 a6
4. Ba4 Nge7
5. d4 exd4
6. Nxd4 Nxd4
7. Qxd4


I'd like to know more about these defenses. What types of games do they produce? Is anyone known for playing them? Are they prone to traps or other tactical considerations?
The Cozio defenses, both with 3....Nge7 (1) and 3....a6 4.Ba4 Nge7 (2), have been played by top grandmasters like Nakamura and Aronian. According to the Game Database of ChessTempo both variations are quite regularly played and equally popular: 1160 games for (1) and 703 games for (2).

Unsurprisingly, both variants are very similar. After (1) white usually plays 4.0-0 g6 5.c3 or 4.c3 immediately and after (2) white also often chooses the plan with c3: 5.c3 or 5.0-0 g6 6.c3. In this case, the variations of (1) and (2) usually transpose into each other.

However, it seems that there are some subtile differences between (1) and (2).


After (1), white has an extra option that is regularly played: 4.Nc3 g6 5.d4 exd4 6.Nd5 Bg7 7.Bg5. After (2), this idea is less common, as black answers 5.Nc3 with 5....d6. Now 6.d4 does not really work: 6....b5 7.Bb3 Nxd4 8.Nxd4 exd4 9.Qxd4? c5! and black wins the bishop after 10....c4.
In (2), white also has an extra option: after 3....a6 white can play 4.Bxc6.




      [FEN ""]
      [StartPly "5"]

      1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 (3...Nge7 4.Nc3 (4.O-O g6 5.c3) 4...g6 5.d4 exd4 6.Nd5 Bg7 7.Bg5) 4.Ba4 (4.Bxc6) Nge7  5.Nc3 (5.O-O g6 6.c3) d6 6.d4 b5 7.Bb3 Nxd4 8.Nxd4 exd4 9.Qxd4 c5