King and Knight Mate: The King Trapped by Its Own Rook Pawn

Bishop or knight plus king cannot mate a lone king. There is one exceptional net for the knight: when the enemy king is stuck in the corner in front of its own rook pawn on the sixth or seventh rank, king and knight can force mate.

Seal the corner. The king holds the two squares next to the corner, and the knight takes away the last flight square. Here 1.Nc1 covers a2 while the king on c2 covers b1 and b2, so the black king on a1 has no move at all.

The pawn mates its own king. With no king move left, Black must push: 1...a2. The pawn plugs the escape square its king needed, and 2.Nb3 is mate. Accuracy matters only because of stalemate: once the pawn sits on a2 the defender has no legal move left, so only that knight check wins. 2.Nd3 and 2.Ne2 are stalemate, and 2.Nxa2 Kxa2 is a dead draw.

In this drill the finish is short but exact. Cage the king with the knight, let the pawn shut the door, and deliver mate. Just as useful is the lesson in reverse: never steer your own king in front of its rook pawn into a net like this.