Kieseritzky Gambit

After 3...g5, the move 4. h4 attacks the pawn chain before Black can support it with ...h6 and ...Bg7, and it practically forces 4...g4. Instead of retreating, 5. Ne5 centralizes the knight, attacks g4 and eyes f7, where Bc4 can add pressure. Because Black is a pawn up, returning one of the advanced pawns is acceptable, and most defenses do so in exchange for activity. Lionel Kieseritzky popularized the line in the 1840s, and Wilhelm Steinitz used it with success. Boris Spassky played it to beat Bobby Fischer at Mar del Plata in 1960, and modern writers treat it as the main line after 3...g5.

The Berlin Defense, 5...Nf6, counterattacks e4 rather than defending g4. Its main line runs 6. Bc4 d5 7. exd5 Bd6, the Anderssen Defense, and Black scores very well with it. The Kolisch Defense, 5...d6 6. Nxg4 Nf6, gives the pawn back to gain a lead in development. 5...Qe7, the Rosenthal Defense, usually regains material but exchanges queens, which leaves the doubled f-pawns as a lasting weakness. In online games the Long Whip, 5...h5, is the most frequent reply. It is regarded as dated and risky because 6. Bc4 forces awkward moves such as ...Rh7 or ...Nh6. Engines rate the starting position as roughly balanced.