Chess Opening Theory/1. d4/1...d5/2. Bf4/2...h5

This sneaky and uncommon sideline sets up a trap to win White's bishop.

At first glance, this move appears strange, developing a flank pawn instead of a piece or central pawn. However, 3. e3? lets Black win the bishop for three pawns after 3...e5! 4. Bxe5 (4. dxe5?! g5 5. Bxg5 Qxg5 6. Qxd5∓) 4... f6 5. Be2 fxe5 6. Bxh5+ Ke7 7. dxe5⩱, and thus White will have to change their usual e3 move and choose one of two responses instead.

3. Nf3 develops the kingside knight and doesn't block the c1-h6 diagonal for the bishop unlike 3. e3. It is quite solid and questions Black's premature h5 pawn push.

3. c4 challenges Black's center and is White's best move, ignoring Black's flank attack and instead focusing on the most important region of the board: the center. This can lead to aggressive play from both sides.