Second-rank defense

The second-rank defense occurs in the pawnless ending of rook against rook and bishop. The stronger side tries to drive the defending king toward the edge and build a mating net, meaning a formation that controls its escape squares and can force checkmate. The defender seeks a stable formation instead of chasing the attacking pieces.

The defending king and rook remain on a line one square in from the edge. This may be the second or seventh horizontal row, called a rank, or a vertical column one square in from either side when the position is rotated. The rook moves near the king, gives timely checks, and blocks routes that would let the attacking rook get behind the king.

It is called passive because the defender gives up space and repeats a structure, not because any waiting move works. Danger increases when the king is pushed too close to a corner, the rook strays too far, or a move lets the bishop control the return square. The attacking pieces may then break the barrier.

The Szén position is another major defense in the same ending, but it uses a different relationship between the kings and requires the rook to defend from the side where its king has more room.