O'Kelly Defense

The O'Kelly Defense answers 4. f3 with 4...c6, leaving the extra pawn on e4 for the moment and covering d5 and b5 before Black commits the queen's bishop. Its chief purpose is a matter of move order: it heads for the Ziegler Defense while denying White the 6. Bd3 option available in that line. After 5. Bc4 exf3 6. Nxf3 Bf5 the game is in the 6. Bc4 Bf5 branch of the Ziegler. White's other tries are less appealing. 5. Nxe4 leads to a Caro-Kann Fantasy Variation structure where White can hope for no more than equality, and other bishop moves let Black reach improved forms of standard gambit lines.

In practice 5. fxe4 is chosen in most games, even though 5...e5, striking at d4, is considered favorable for Black; White nonetheless scores well in online play, and the engine judges the position roughly level. The line also has independent content. After 5. Bc4 Bf5 White must play precisely, though 6. g4 Bg6 7. g5 Nd5 8. fxe4 Nxc3 9. bxc3 appears to give adequate play. Evgeny Bareev employed an early ...b5 against Nigel Short and obtained the better position.