Discovered attack

A discovered attack occurs when one of your pieces has been blocking a rook, bishop, or queen and moves away, leaving that piece's line open. The piece behind it then attacks along a vertical file, a horizontal rank, or a diagonal. The important feature is not merely the front piece's move, but the attack that appears behind it.

The tactic is often powerful because the moving piece can create a threat of its own. It may capture something, attack a valuable piece, or give check, which means directly attacking the king, while the piece behind it threatens a different target. When two threats appear at once, the result is a double attack, and the opponent may be unable to answer both with one move.

The opened line must lead to a real target. Moving a blocker is not useful by itself if the rook, bishop, or queen behind it gains nothing. A battery, an alignment of two or more rooks, bishops, or queens on the same line, can prepare especially dangerous discovered attacks.