Pin Chess Puzzles

Background reading

Pin (chess)

In chess, a pin is a tactic in which a defending piece cannot move out of an attacking piece's line of attack without exposing a more valuable defending piece. Moving the attacking piece to effect the pin is called pinning; the defending piece restricted by the pin is described as pinned. Only a piece that can move any number of squares along a horizontal, vertical, or diagonal line (i.e. a bishop, rook, or queen) can pin. Any piece can be pinned except the king. The pin is one of the most powerful chess tactics. The inverse of a pin is a skewer, in which a more valuable piece under direct attack may move to expose a less valuable piece to an attack.

Absolute pin

An absolute pin is one where the piece shielded by the pinned piece is the king. In this case it is illegal to move the pinned piece out of the line of attack, as that would place one's king in check (see diagram). A piece pinned in this way can still give check or defend another piece from capture by the opposing king.

Relative pin

A relative pin is one where the piece shielded by the pinned piece is a piece other than the king, but typically is more valuable than the pinned piece. Moving such a pinned piece is legal but may not be prudent, as the shielded piece would then be vulnerable to capture if the pinned piece moving does not put the opponent’s king in check.

Partial pin

Independently of whether it is absolute or relative, a pin might be a partial pin, in which the pinned piece can still move along the line of the pin, and it might be able to capture the piece that is pinning it, but it cannot leave that line. For example, a rook or queen can be partially pinned along a file or rank, or a bishop or queen can be partially pinned along a diagonal. Capturing the pinning piece can still be advantageous to the pinning player, as in the example diagram (the pinning rook is defended, so capturing it with the queen would lose material). A queen can only ever be partially pinned, as she can move in any linear direction, while a knight can only be completely pinned due to its unique movement. The pawn is a more complex case; due to its limited and conditional movement, whether a pin on a pawn is partial depends on the line and direction of the pin and on whether there are opposing pieces available for it to capture. It is possible for two opposing pieces to be partially pinning each other.

Situational pin

Sometimes a piece may be considered to be in a situational pin. Like a relative pin, a situational pin does not legally restrict the piece from moving, but moving the pinned piece out of the line of attack can result in some detriment to the player (e.g. checkmate, immediate loss of the game, occupation of a critical square by the opponent, etc.). Consider the diagrammed position with White to move. The black bishop on d5 is unprotected and White can capture it with 1.Nxd5; however, White should not play the capture or otherwise move the knight, due to the skewer attack 1...Rb1+ winning White's rook (the king is forced to move, then 2...Rxh1). It can be said that the white knight is "pinned to the b1-square" rather than pinned to a piece.

Cross-pin

A cross-pin consists of two or more pins, of any type, on the same piece. As there is only one king per side, only one of the pins can be absolute, but there are otherwise no restrictions on the types of pins involved.