Checkmate
A knight delivers checkmate to an enemy king that is completely surrounded by its own pieces.
A knight delivers checkmate to an enemy king that is completely surrounded (smothered) by its own pieces. Because the knight can leap over pieces, the blocking friendly pieces offer no protection and instead seal the king's doom.
The most famous manifestation is “Philidor’s Legacy,” a multi-move tactical sequence involving a queen sacrifice (Qg8+! Rxg8) to force the opponent’s rook to smother its own king, followed by Nf7#.
See also:Sacrifice·Arabian Mate