Even though this move looks very bad, because White can go 5. Nxe5 and it's unclear how to save the f7 pawn and the rook on h8, that's not like that. Yes, after 5. Nxe5 the f7 pawn would be captured in any variant, but black can go 5... Qe7! From now, there are a couple of ways the game can continue:

6. Nxf7!? - the most logical move. It doesn't just capture the pawn, but also trapped the rook in the corner. But this move is awkward because of 6... Qxe4 and after 7. Kf1 Qxc2 the rook will be regained, or a deadly 6... d5! move.

6. Bxf7+! - the best move in this position. Here Black must go 6... Kf8! Now the move 7. Bxg8 is forced because the knight on e5 is attacked. After 7... Kxg8, the knight has to go somewhere, and after 8... Qxe4 black has a better position.

Another option would be to go 5. Be3, avoiding all the stuff with 5. Nxe5. This is the most solid and best by the computer move.

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1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.d4 Nxd4

Wikipedia has related information at Italian Gambit.

• Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.