Halasz-McDonnell Gambit

Instead of recapturing on d4, White uses the fact that Black's e-pawn no longer covers f4 to advance the f-pawn and claim space on the kingside, much as in a King's Gambit. The price is a pawn, and the d4-pawn becomes a long-term problem for White. While it stands, it controls c3, so White cannot easily bring a knight to defend e4.

Black's most common reply is 3...Nc6, protecting the extra pawn. After 4. Nf3, Black can strike with 4...d5, opening lines against the e4-pawn and taking over the initiative. Engines give Black a clear advantage, and theory holds that White lacks full compensation against accurate defense, although the line has never been refuted outright. The immediate 3...d5 scores best for Black in practice, and 3...c5 reinforces the d4-pawn. The Crocodile Variation, 3...Bc5 4. Nf3 Nc6 5. c3, has White undermining the pawn chain at once. Despite the engine verdict, White scores slightly better than Black in online games, where the unfamiliar positions cause practical difficulties.