Four knights - Scotch - 4...exd4
1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. d4 exd4
White advances the king's pawn to e4. Black pushes the king's pawn to e5. White develops the knight to f3.
Black develops the knight to c6. White jumps the knight to c3. Black moves the knight to f6.
White advances the queen's pawn to d4. Black captures on d4 with the king's pawn.