Trying to keep the pawn with ...b5
1.d4 d5 2.c4 c6 3.Nf3 Nf6 4.Nc3 dxc4 5.a4 b5 6.axb5 cxb5 7.Nxb5
- The mistake
- Holding on to the c4 pawn with …b5 after a4.
- Why it costs
- The a-file opens behind the pawn on b5, and it cannot be held: both 7.Nxb5 and the quieter 7.b3 win the material back, and Black is left with a broken queenside and a bishop on c8 that still has not moved. The pawn on c4 was never keepable — a4 is the move that proves it.
- Instead
- 5…Bf5, the main line. The pawn goes back and Black gets the bishop outside the pawn chain, which is worth more than the pawn ever was.