Reversed Brooklyn Defense, Brooklyn Benko Gambit

This line arises from the Reversed Brooklyn Defense, where White meets 1. g3 e5 2. Nf3 e4 with the retreat 3. Ng1. The retreat mirrors the Brooklyn Defense to Alekhine's Defense, in which Black's knight returns to its home square. After 3...Nf6, the move 4. b4 puts the b-pawn en prise to Black's dark-squared bishop. In return White gains space on the queenside while the advanced e4-pawn is left to be targeted later. The gambit is a rare sideline.