Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bc4/3...f5

= Rousseau Gambit =

3...f5

 * White has two strong choices: The first is to support with 4. d3. This results in a reversed King's Gambit Declined, dangerous for both sides.  Black often places their pieces in typical Giuoco Piano fashion and waits for white to castle kingside before pushing f4.  Black will attack the kingside and white will attack in the center.
 * White can also play 4. d4. Black responds by taking one of the pawns.  If 4...exd4 then 5. e5 and black will play 5...d5 or 5...d6 allowing the center to open; white quickly castles with a huge initiative.  If 4...fxe4 then 5. Nxe5 and white is in an improved version of the main line of the Latvian Gambit.
 * Taking with 4. exf5? is a common mistake by beginners. After 4...e4, white has to find the piece sacrifice 5. Nd4!, planning to respond to 5...Nxd4?? with Qh5+ and going into massive complications that favor white.  But if black plays the correct 5...Nf6 then black already has a small advantage.  Attempting to defend the pawn with 4. Nc3?? is a losing blunder.
 * Taking with 4. exf5? is a common mistake by beginners. After 4...e4, white has to find the piece sacrifice 5. Nd4!, planning to respond to 5...Nxd4?? with Qh5+ and going into massive complications that favor white.  But if black plays the correct 5...Nf6 then black already has a small advantage.  Attempting to defend the pawn with 4. Nc3?? is a losing blunder.
 * Taking with 4. exf5? is a common mistake by beginners. After 4...e4, white has to find the piece sacrifice 5. Nd4!, planning to respond to 5...Nxd4?? with Qh5+ and going into massive complications that favor white.  But if black plays the correct 5...Nf6 then black already has a small advantage.  Attempting to defend the pawn with 4. Nc3?? is a losing blunder.


 * Key themes for White at this point are to attack Black's kingside using the light bishop and to resist attempts by black to simplify the position via exchanges. Exchanges involving White's light bishop are particularly suspect.  The best advice for Black is to not play this gambit, as it's considered to be refuted.

Theory table
.

1.e4 e5 2.Nf3 Nc6 3.Bc4 f5