Chess Opening Theory/1. d4/1...d5/2. c4/2...c6/3. Nc3/3...dxc4/4. e3/4...b5/5. Nxb5

5.Nxb5?
This clever attempt to win material is a huge mistake, and gives black two ways to get an advantage, the first one being the best. In one way, the queen will get trapped on a8, and black will build a cage and try to win the queen. Black can also return the piece, with a lead in development and huge queenside space advantage.

a4 is better, when b4 Ne4 Qd5 is the normal continuation and white will try to rip black's space-gaining queenside to bits. Black would try to strengthen it.