Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...a6/4. Ba4/4...Nf6/5. O-O/5...Be7/6. Re1

=Ruy Lopez Main Line=

Now the White's own e-pawn is defended, the threat Bxc6 followed by Nxe5 winning a pawn becomes a serious problem for Black.


 * 6...b5 permanently cuts out any of that nonsense.

There's also
 * 6...d6, the Averbakh Variation. It looks like Black has just forgotten which order to play the moves in, because in most Closed Ruy Lopez variations White will eventually bring the bishop back to c2, and 6...d6 allows White to play Ba4-c2 in a single move thus saving a tempo. On the other hand, trying to take advantage of that fact with 7.c3 gives Black a spare tempo of her own to play ...Bg4, and whenever a bishop appears on g4 in the Closed Ruy Lopez you know White is going to have to play d3 and bring the queen's knight across to the kingside to drive the bishop away before considering d4. On the other other hand, Magnus Carlsen voluntarily plays d3 instead of d4 even without a bishop on g4, so the current verdict seems to be that 6...d6 loses a tempo for no reason.

Theory table
.

'''1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. O-O Be7 6.Re1'''