Bird's opening - Swiss gambit
1. f4 f5 2. e4 fxe4 3. Nc3 Nf6 4. g4
White moves the f-pawn to f4. Black plays the f-pawn to f5. White moves the king's pawn to e4.
Black captures on e4 with the f-pawn. White develops the knight to c3. Black develops the knight to f6.
White advances the g-pawn to g4.