Zatox wrote on 03/13/08 at 14:07:04:

I am not sure that this is really so; quite a few not exactly weak players have reacted in that way. Of these, GM Kozul is a particularly interesting example, because he must have given much thought to 3.Bb5, as he more or less "re-invented" the reply 3…Na5 to the Rossolimo in the mid-nineties – and extremely successfully at that.

So, seeing him play 3…a6 in a couple of games in 2002, 2004 and 2006 was some food for thought. Here is one of his efforts: 

[Event "EU-ch 7th"]
[Site "Kusadasi"]
[Date "2006.04.04"]
[Round "10"]
[White "Belov,Vladimir"]
[Black "Kozul,Zdenko"]
[Result "1/2"]
[Eco "B30"]
1.e4 c5 2.Nf3 Nc6 3.Bb5 a6 4.Bxc6 dxc6 5.d3 Qc7 6.Nbd2 a5 7.a4 e5 8.Nc4 f6 
9.Nh4 Be6 10.0-0 0-0-0 11.Qe1 b6 12.Qc3 Ne7 13.Qb3 Bxc4 14.Qxc4 Kb7 15.Nf3  1/2

It seems to me that 3…a6 has a definitive advantage over every other of Black's 3rd moves, i.e., White is virtually forced to play 4.Bxc6. (4.Be2 would be ridiculous, of course, and 4.Ba4?? is a blunder owing to 4...b5 5.Bb3 c4. Don't laugh – it has happened even in corresponding games!)

Why does the forced 4.Bxc6 constitute an "advantage" for Black? Well, after any other 3rd move by Black, White has essentially three different strategies at his disposal:
1) Bxc6 immediately or at a slightly later stage, "ruining" Black’s pawn structure
2) playing Ba4, c3 and Bc2 (as in the Ruy Lopez)
3) playing Re1 and Bf1

As Black, it is not so easy to cope with all of these different approaches, but 3…a6 almost always allows Black to reach one and the same type of pawn structure after the further moves 4…dxc6, 5…Qc7 and 6…e5. Black can then continue either solidly (…0-0) or aggressively (…0-0-0, …f6, …g5, …h5). 

Here are two examples:

[Event "Oviedo rapid45"]
[Site "Oviedo"]
[Date "1992.??.??"]
[Round "6"]
[White "Kovalevskaya,Ekaterina"]
[Black "De la Villa Garcia,Jesus Maria"]
[Result "0-1"]
[Eco "B30"]
1.e4 c5 2.Nf3 Nc6 3.Bb5 a6 4.Bxc6 dxc6 5.0-0 Bg4 6.d3 Qc7 7.Nbd2 e5 8.Nc4 f6 
9.a4 a5 10.Bd2 Ne7 11.Qe2 Ng6 12.h3 Be6 13.Nh2 Be7 14.Ne3 Qd7 15.Qh5 Bd8 16.Nf5 0-0 
17.Be3 b6 18.Ng3 Bc7 19.Qd1 Nf4 20.Nh5 f5 21.Ng3 Nxh3+ 22.gxh3 f4 23.Nf5 Bxf5 24.exf5 Qxf5 
25.Bd2 f3 26.Qxf3 Qxf3 27.Nxf3 Rxf3 28.Kg2 Raf8 29.Rae1 R8f5 30.Re4 Kf7 31.Be3  0-1

[Event "Muensterland op"]
[Site "Senden"]
[Date "2005.10.02"]
[Round "3"]
[White "Ottens,Stephan"]
[Black "Gutman,Lev"]
[Result "1/2"]
[Eco "B30"]
1.e4 c5 2.Nf3 Nc6 3.Bb5 Qc7 
(Note the move order. 3…a6 4.Bxc6 dxc6 5.0-0 Qc7 leads to the same position as in the game.) 
4.0-0 a6 5.Bxc6 dxc6 6.h3 e5 7.d3 f6 8.Be3 g5 9.Nbd2 g4 10.Nh4 Nh6 11.f4 gxh3 12.Qh5+ Qf7 13.Qxf7+ Nxf7 14.f5 Rg8 15.Kf2 hxg2 16.Nxg2 b5 
17.Rh1 Rg7 18.Rh2 c4 19.dxc4 Bb7 20.c5 0-0-0 21.b4 a5 22.a3 Ng5 23.Nh4 Rgd7 24.Nhf3 h6 
25.Ke2 Kc7 26.Nxg5 hxg5 27.Nb3 a4 28.Nd2 Ba6 29.Nf1 Bc8 30.Ng3 Rf7 31.Rah1 Bd7 32.Rh7 Be8 
33.Rh8 Be7 34.R1h7 Rxh7 35.Rxh7 Rd7 36.Nh5 Bd8 37.Rxd7+ Kxd7 38.Ng3 Bf7 39.Kf3 Ba2 40.Kg4 Ke7 
41.Kf3 Bb1 42.c3 Bd3 43.Bd2 Kf7 44.Nh1 Kg7 45.Nf2 Bc2 46.Ng4 Bd1+ 47.Kg3 Be2 48.Be1  
1/2

As for the attack with …f6, …g5 and …h5, recall the famous game Shirov-Kramnik, Novgorod 1994. Kramnik didn't play 3…a6, but the position after Black's 12th move could also have emerged from a 3…a6 move order:

[Event "Novgorod"]
[Site "Novgorod"]
[Date "1994.08.??"]
[Round "7"]
[White "Shirov,Alexei"]
[Black "Kramnik,Vladimir"]
[Result "0-1"]
[Eco "B31"]
1.e4 c5 2.Nf3 Nc6 3.Bb5 g6 4.Bxc6 dxc6 5.h3 e5 6.d3 f6 7.c3 Nh6 8.0-0 Nf7 
9.Be3 g5 10.Ne1 Be6 11.Nd2 h5 12.a3 a5 13.Qe2 b6 14.Nc2 Ra7 15.d4 cxd4 16.cxd4 Rd7 
17.dxe5 Nxe5 18.Rfd1 Be7 19.Nf1 Bc4 20.Rxd7 Qxd7 21.Qd2 Bd3 22.Qc3 Bxe4 23.Ng3 Bd5 24.Bxb6 h4 
25.Ne2 g4 26.Nf4 Be4 27.Re1 Qf5 28.Ne6 Rg8 29.Ncd4 Nf3+ 30.Kf1 Bd3+ 31.Re2 Bxe2+ 32.Kxe2 Qe4+ 
33.Qe3 Nxd4+ 34.Nxd4 Qxe3+ 35.Kxe3 gxh3 36.gxh3 Rg5 37.Nxc6 Bc5+ 38.Bxc5 Rxc5 39.Nd4 a4 40.Kd3 Rc1 
0-1

It is also instructive to compare the position after 3…a6 4.Bxc6 dxc6 with the position that occurs after 1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Bxc6 dxc6. In the Ruy Lopez Exchange, White often plays an early d4, as then White will be left with a pawn majority on the king side. If White played an early d4 in the Rossolimo after 3…a6 4.Bxc6 dxc6, the pawn structure would become symmetrical again, with Black still having the bishop pair. 

It is also possible for the initial pawn structure of the Ruy Lopez Exchange to transform into that of the Rossolimo. Have a look at this game:

[Event "Thessaloniki ol (Men)"]
[Site "Thessaloniki"]
[Date "1988.11.??"]
[Round "1"]
[White "Mahayri,Sabri M"]
[Black "Ivanchuk,Vassily"]
[Result "0-1"]
[Eco "C68"]
1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Bxc6 dxc6 5.d3 f6 6.Be3 c5 7.Nbd2 Be6 8.0-0 Qd7 
9.a4 a5 10.Nc4 b6 11.Nfd2 g5 12.Nb1 Ne7 13.Nc3 h5 14.Qe2 Ng6 15.f3 Be7 16.Kh1 Bd8 
17.Rad1 c6 
(Now we have reached the Rossolimo pawn structure!)
18.b3 Bc7 19.Qf2 Kf7 20.Ne2 Rad8 21.Qe1 Kg7 22.Qc3 Nf4 23.Ng1 Bf7 24.Bf2 Ne6 
25.h4 Qe7 26.Bg3 Nf4 27.Ne3 Be6 28.Qe1 Qd7 29.Ne2 Ng6 30.Qf2 Rdf8 31.Qe1 Bd8 32.Nc4 b5 
33.axb5 cxb5 34.Nxa5 gxh4 35.Bf2 Be7 36.Ra1 h3 37.gxh3 Bxb3 38.Kh2 Bxc2 39.Ng3 Nh4 40.Qe3 Bxd3 
41.Rfd1 c4 42.f4 Kf7 43.f5 Qd4 44.Nc6 Qxe3 45.Bxe3 Ra8 46.Kg1 Nf3+ 47.Kf2 Nd4 48.Nxd4 exd4 
49.Bxd4 h4 50.Ne2 Bxe4 51.Nc3 Bc6 52.Re1 Rxa1 53.Rxa1 Rh5 0-1

Recently i've been having some problems against this line. (With black). I know moves like 3...a6 lead to horrible positions for black and 3...g6 and 3...e6 are the most played moves in this position but I'm still having many difficulties against it. Could anyone give me some hints and or good lines?