After 3. Bb5
, black plays
a6
a6
puts the question to the bishop. If he takes your knight, recapture with the d
pawn. Black has a very strong game at this point. Normally you capture toward the center, but in this case, you can play c6
to c5
and control the d4
square. d4
is very important to control in the Ruy Lopez.
What you see most often after a6
is the bishop retreating to a4
. White may play c3
later in the game to give his bishop a square (c2
) to back up into. You see the same thing happening on the other side of the board with f3
in the Queen's Indian, giving white's bishop on g5 the option to back up to Bh4
and then retreat to Bf2
.
(White playing c3
also prepares for the d4
push, common for white in the Ruy Lopez. c3
protects the d4
pawn.)
Nf6
You're probably going to see Nf6
eventually. After Bb5
you might see it right away. Or you'll see it after 3. Bb5 a6 4. Ba4 Nf6
. What does Nf6
do for black? It attacks the unguarded e4
pawn with the knight. But white doesn't have to worry here. Instead, white castles O-O
. Why?
Take a moment to play this out on a board:
[FEN ""]
1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. O-O Nxe4 6. Re1
Black is screwed after Re1
. Notice that the rook is staring down the king. The pawn/knight are pinned. If black retreats the knight back to Nf6
, now white takes the knight. Black recaptures the bishop. Now the pawn on e5
is unguarded. Nxe5
and you have a deadly discovered check on black's king when the knight moves.
[FEN ""]
1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. O-O Nxe4 6. Re1 Nf6 7. Bxc6 dxc6 8. Nxe5
it's all over for black.
That's how Capablanca describes the Ruy Lopez in his book Chess Fundamentals (if I remember correctly).
3...f5
can be a fun line to play.