interference

The idea

An enemy piece defends an important square from a distance — along a line or a diagonal. That connection is cut: a piece is placed between the defender and the square. The link is broken and the defence stops working.

How it looks

There are two ways to do it.

First: put your own piece directly in harm's way, on the defender's line. If your opponent takes it, he blocks his own line with his own piece. If he does not, the decisive blow goes through.

Second: force your opponent to occupy the line himself, with his own piece — usually by check or by an attack.

How to spot it

Find where the defence of the square you want comes from. Then look at the squares between the defender and the target: can you put anything there?

Often confused with

The tactic is subtle and looks like a blunder: a piece is placed where it can be captured. Until you calculate to the end, the move simply looks like a mistake.