Nimzowitsch Defense: Colorado Countergambit Accepted

The Nimzowitsch Defense: Colorado Countergambit Accepted is a chess opening classified under ECO code B00 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 Nc6 2. Nf3 f5 3. exf5. The resulting position leaves black to move.