Undermining (chess) Undermining (chess) Undermining (also known as removal of the guard, or removing the defender) is a chess tactic in which a defensive piece is captured, leaving one of the opponent's pieces undefended or under-defended. The opponent has the unpalatable choice of recapturing or saving the undefended piece. A possible response is to sacrifice the piece whose defense was undermined before capturing the piece which just took the defender. Kramnik–Topalov in the seventh round of the 2004 Linares chess tournament reached the diagrammed position with White to play. The black knight on a4 is defended only by the black pawn on
Chess is under attack, or a stalemate (a draw) if the king is not. Each chess piece has its own way of moving. In the diagrams, the dots mark the squares where the piece can move if there are no intervening piece(s) of either color. Once in every game, each king is allowed to make a special move, known as "castling". Castling consists of moving the king two squares along the first rank toward a rook (which is on the player's first rank) and then placing the rook on the last square that the king has just crossed. Castling is permissible