Unpinning

A pin occurs when a piece in front of another cannot move freely because doing so would expose the king, a more valuable piece, or a critical point. Unpinning changes that relationship so the front piece regains mobility or moving it no longer has a serious consequence.

In an absolute pin, the piece shields the king from a line attack. Moving it off the line and leaving the king in check would be illegal. In a relative pin, moving the piece is legal, but it normally allows the piece behind it or another important advantage to be lost.

Common ways to unpin

• Move the king or valuable rear piece so that the target of the pin no longer exists.
• Capture or drive away the pinning piece, including with the pinned piece when that capture is legal.
• Interpose another piece on the attacking line so the pinned piece can move afterward.
• In a relative pin, create a stronger tactical threat or accept the loss of the rear target when the compensation is sufficient.

Unpinning need not be a passive defensive move. A tactical reply, based on a concrete short-range sequence, may exchange pieces, force a response, or turn the opponent's pressure into activity.