Chess Opening Theory/1. d4/1...d5/2. c4/2...c6/3. Nc3/3...dxc4/4. e3/4...b5/5. Nxb5/5...cxb5/6. Qf3/6...Nc6/7. Qxc6/7...Bd7/8. Qf3/8...e5/9. dxe5

9.dxe5?
This move accepts the sacrifice, but this is another mistake, allowing Black a crushing attack. In a situation like this, it is more important to develop and stop Bb4+ with a move like Bd2. This also opens the d-file, this amplifying the power of Black's attack. The best move to attack is Bb4+.