Colorado Countergambit

The Colorado Countergambit is a sharp answer to the Declined Variation of the Nimzowitsch Defense. Schiller called it the Lean Variation or Colorado Counter. The flank thrust 2...f5 aims to lure White's e-pawn away so that Black can follow with ...d5 and hold two central pawns against one. The cost is a loosened kingside, and theory regards the line as dubious. The engine gives White a clear advantage, although Black scores slightly better than White in online games.

Accepting with 3. exf5 is the most common reply. After 3...d5, White does best to return the pawn with 4. d4 Bxf5, reaching an open game in which Black's king remains the lasting weakness. Attempts to keep the extra pawn are less convincing. 4. Bd3 obstructs White's own d-pawn. The tricky 4. Nh4 sets a trap: after 4...e5 5. Qh5+ Black must move the king, because 5...g6 6. fxg6 Nf6 7. g7+ Nxh5 8. gxh8=Q wins material for White. White can also decline with 3. e5, the second most popular move, or simply develop with 3. Nc3.