blocking

The idea

A piece has nowhere to go because its own pieces are in the way. As long as nobody attacks it, no harm is done. But the moment it is attacked, it cannot escape.

How it looks

The most common case involves the king. He has one free square left, so there is no mate. You sacrifice to force your opponent to occupy that square with his own piece: he captures, his piece blocks the escape — and mate works.

But blocking is not only about kings. A queen goes into a corner with her own pawns around her. Untouched, she is merely badly placed. Attacked, she is lost, because there is nowhere to run.

How to spot it

Count escape squares. If an important piece has none, or only one, look for a way to attack it.

Count the enemy king's escape squares especially carefully: very often the only thing missing for mate is one square being occupied.

Often confused with

A trapped piece. The distinction is simple: in blocking the path is closed by own pieces, in trapping by enemy pieces.