Chess Opening Theory/1. d4/1...d5/2. c4/2...e6/3. Nc3/3...c6/4. e4/4...dxe4/5. Nxe4/5...Bb4

Semi-Slav defence: Marshall gambit Marshall gambit 5...Bb4+ This move is Black's best option to fight for an advantage. It forces White to either gambit the d4 pawn for activity, or to retreat the knight back to c3, "losing" a tempo in the process. /6. Bd2/ is the main move, blocking the check and attacking Black's bishop at the same time. This does however block the white queen from defending the d4 pawn, allowing 6...Qxd4, which gambits the pawn in exchange for quick development and active pieces. /6. Nc3/ is the Forgotten variation, a sideline where White holds onto the d4 pawn, keeping material equal. 6. Nd2? is a mistake, since it contains all the drawbacks of 6. Bd2 (losing d4) and none of the advantages (getting a very active dark-squared bishop). To add insult to injury, it also hampers the development of White's queenside by locking up the c1 bishop. Theory table 6. Bd2 Qxd4 7. Bxb4 Qxe4+ unclear Forgotten variation 6. Nc3 c5 7. a3 Ba5 6. Nd2 Qxd4 7. Nf3 Qd8 - See also Semi-Slav Defense Marshall_Gambit