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 rook behind the screen

8

7

6

5

4

3

2

a1

b

c

d

e

f

g

h

Start

Bb7+

The friendly bishop on e4 cuts off the rook's line before e8.

The file is closed

The white bishop on e4 occupies the file between the rook on e1 and the king on e8. That interposition prevents the rook from giving check along the file.

1. The friendly bishop on e4 cuts off the rook's line before e8.

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.