Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bc4/3...Bc5/4. b4/4...Bb6

4... Bb6
Black declines the gambit by playing 4... Bb6. Black refuses to give White the opportunity to gain tempo and hangs onto the center. However, White can play /5. a4/ with plans to play 6. a5 later on to trap the bishop.