Rousseau Gambit

With 3...f5 Black hits e4 in King's Gambit fashion, hoping to deflect White's e-pawn and claim the center with tempo. The cost is a loosened a2-g8 diagonal, exactly where White's bishop already stands, so Black's king finds castling short awkward and a knight jump to g5 becomes a recurring threat. The line is named after the French master Eugène Rousseau and is also known as the Ponziani Countergambit. It resembles the Latvian Gambit, but with the bishop on c4 and the knight on c6 already committed.

4. d3 is the most played reply. It simply defends e4 and leaves the f5-pawn hanging for later, giving a King's Gambit Declined with the colors reversed and an extra tempo for White. Black typically develops along Giuoco Piano lines; 4...Bc5 transposes to the Lucchini Gambit. A common plan is to hold back ...f4 until White has castled kingside, then turn the f-pawn and pieces against the white king while White seeks play in the center. White keeps the light-squared bishop, avoids exchanges that would relieve Black, and aims at the weakened kingside.

4. d4 is the most forcing answer. After 4...exd4 5. e5 Black usually opens the position with ...d5 or ...d6, and White castles quickly with a strong initiative. After 4...fxe4 5. Nxe5 the play resembles a favorable version of the Latvian main line for White; the Bilguer Handbuch continued 5...d5 6. Bb5 Ne7 7. O-O a6 8. Bxc6+ bxc6 9. f3 Bf5 10. Nc3 with an edge for White. Nineteenth-century practice also covered 4...d6, as in Morphy–Worrall, London 1859, which went 5. dxe5 dxe5 6. Qxd8+ Kxd8 7. Bg5+ Nf6 8. Nc3 with the better endgame for White.

The natural capture 4. exf5 is almost as popular as 4. d3 but suits Black best. After 4...e4 White must play 5. Nd4, since 5...Nxd4 runs into 6. Qh5+; the correct 5...Nf6 6. Nxc6 leads to an unclear game. Defending the e-pawn with 4. Nc3 instead is regarded as a serious mistake.

The engine gives White a clear advantage, and the gambit is generally considered refuted. In online games, however, Black wins slightly more often than White overall, and scores especially well when White grabs the pawn with 4. exf5.