With 4. Bc4, white temporarily forgoes recapturing the d4 pawn, instead developing the light-squared bishop to the most active square targeting the f7 pawn. White usually intends to follow up with 5. c3 on the next turn, continuing in an aggressive style.

Black should continue developing their pieces:

4...Nf6 is the most played move, developing the knight and attacking the pawn on e4. This position can also arise out of the Two Knights Defence in the Italian Game (after 1. e4 e5 2. Nf3 Nc6 3. Bc4 Nf6 4. d4 exd4). After this move, white usually responds either with 5. e5 or continues playing in gambit-style fashion with 5. O-O.

4...Bc5 is the second most played move, developing the dark squared bishop and also defending the pawn on d4. The downside of this move is that the bishop could become a potential target on c5, especially to an eventual Qh5 which puts pressure on both f7 and c5.

4...Bb4+ is also possible. Black checks the king and white always blocks with 5. c3 on the next move. This usually responds in white sacrificing either one or two pawns in exchange for rapid development and active pieces targeting black's king.

4...Be7 is Black's final good option to develop the bishop. This transposes to a variation of the Hungarian Defence in the Italian Game, though the bishop is not optimally placed on e7, and as a result, black needs to be careful about potental checkmate threats.

For explanation of theory tables, see theory table and for notation, see algebraic notation..

1. e4 e5 2. Nf3 Nc6 3. d4 exd4 4. Bc4

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