Alekhine Defense: O'Sullivan Gambit

The Alekhine Defense: O'Sullivan Gambit is a chess opening classified under ECO code B03 in the Semi-Open Games family, where Black responds to 1.e4 with something other than 1...e5, including the Sicilian Defense, Caro-Kann, and Pirc. It is reached after 3 moves: 1. e4 Nf6 2. e5 Nd5 3. d4 b5. The resulting position leaves white to move.