The position in the diagram occurs after 3.Nc3 Nf6 4.Bg5 Be7 5.e5 Nfd7. Now there are two main variations.
-
After 6.Bxe7 Qxe7, the players will usually castle on opposite sides. A typical continuation is
7.f4 O-O 8.Nf3 c5 9.Qd2 Nc6 10.O-O-O f6 11.exf6 Qxf6 12.g3 cxd4 13.Nxd4.
Black has used both the ...c5 and ...f6 ideas against the Pawn chain. The e-Pawn is weak, but easily defended. White has no attacking possibilities on the Kingside and must be careful about ...e5. Before Black can play ...e5, the d-Pawn must be adequately protected. White has difficulty castling Kingside: 10.g3 f6 11.exf6 Nxf6 12.Bg2 cxd4 13.Nxd4 e5.
-
After 6.h4, Black can accept the Pawn sacrifice:
6...Bxg5 7.hxg5 Qxg5 8.Nh3 Qe7 9.Nf4 Nc6 (if 9...a6 10.Qg4 g6 11.O-O-O, when the Rook on the h-file is more valuable than the extra h-Pawn) 10.Qg4 g6.
There are many ways to refuse the sacrifice: 6...O-O 7.Bd3 c5 8.Nh3 g6 (but not 8...cxd4 9.Bxe7 Qxe7 10.Bxh7+) 9.f4; 6...c5 7.Bxe7 Kxe7 (7...Qxe7 8.Nb5) 8.f4 Nc6 9.dxc5 Nxc5 10.Qg4 Kf8 11.O-O-O, followed by Rh3 and Rg3; and 6...a6 7.Qg4. One of the best is 6...f6 7.Bd3 (if 7.exf6 Nxf6, or 7.Qh5+ Kf8 8.exf6 Nxf6 9.Qf3) 7...c5 8.Qh5+ Kf8 9.exf6 Nxf6 10.Bxf6.
