Two knights versus pawn ending

This ending is paradoxical. A king and two knights cannot force checkmate against a lone king, although mating positions exist. The defender can avoid entering them voluntarily, and at some moments the lack of any legal move would produce stalemate, an immediate draw when the player to move has no legal move and the king is not in check.

The defending pawn can remove that escape. While it remains on the board, its side may be forced to move it, supplying the extra move needed to complete a mating net, a formation that confines the king and can force checkmate. Having an extra pawn can therefore turn an otherwise defensible position into a loss.

Basic technique

1. One knight blockades the pawn, preventing it from reaching the last rank and becoming another piece.
2. The king and the other knight drive the defending king toward a suitable corner or mating area.
3. When the net is ready, the blockading knight leaves the pawn and joins the mate. The forced pawn move supplies the extra move that was missing.

Not every position is won. The square where the pawn is blockaded, both kings, the second knight, and whose turn it is are decisive. The second Troitsky line relates those squares to the fifty-move rule, which permits a draw claim after fifty moves by each player without a pawn move or capture.

The method contains forms of zugzwang, because the defender loses by being compelled to make the pawn move at a specific moment. If the attacking side captures the pawn too early, the game returns to two knights against a lone king and the winning chance normally disappears.