Copenhagen Defense

The Copenhagen Defense, sometimes spelled Copenhagen Defense, arises in the Double Danish after 4...cxb2 5. Bxb2 Bb4+. Black keeps both extra pawns and develops a piece with check. This gains a tempo for a side that is behind in development and prepares kingside castling. The drawback is that the bishop is committed to b4, where it can become a target for a later Qb3. That queen move also lines up with the c4-bishop against f7. White must deal with the check at once and has three practical ways to do it. The most frequent is 6. Nc3, which blocks with a developing move. The next most common is 6. Nd2, which keeps the c-pawn's square free and avoids doubled pawns on c3. The rarer 6. Kf1 gives up castling rights so that White's pieces stay unpinned. These are also the moves engines prefer. The engine assessment is close to equal, with a faint lean toward Black. In online play White nonetheless wins clearly more often than Black, because the defender has to handle the open b-, c-, d- and e-files while White's two bishops bear down on the kingside.