Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bc4/3...Nf6/4. Ng5/4...Nxe4/5. Bxf7/5...Ke7

= Two Knights Defence =

5... Ke7
In this position, White must make one more critical move to retain their advantage. If Black manages to trade knights with 6...Nxg5, Black will be able to stabilize their position.

The move 6. d4! prevents this as 6...Nxg5 7. Bxg5 skewers the king and queen. Black capturing the d-pawn is now the least of their worries as White can begin to mount a powerful offensive.

Theory table
'''1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 Nxe4 5. Bxf7+ Ke7'''