Interference in chess

Interference: what is it

Interference is a tactic where you put your piece (or pawn) on the line of an enemy piece. The blocked piece loses its connection to what it was protecting or attacking.

Most often you block the lines of long-range pieces: rooks, bishops and queens. Interference can come with a check, with a capture or with a quiet threat.

When interference works

Interference is used in three situations:

  1. An enemy long-range piece protects a key piece or square, so you need to block the line of defense.
  2. An enemy piece holds back a threat of mate or a capture, and interference switches it off.
  3. Two of the opponent's pieces have crossing lines: a sacrifice on that square blocks both at once (the Novotny theme).

For the interference to succeed, the blocking piece must not be captured right away, or its loss must be justified by the main idea.

Why it works

Every long-range piece "works" only along a straight line. Put any piece or pawn on that line, and the connection to the target is cut off until the blocking piece moves away.

Important: make sure the opponent cannot both remove your blocking piece and keep the defense. If they have a move that does both, the tactic will not work.

How to find interference

  1. Find the opponent's long-range piece that gets in the way of your attack: it protects a square, a piece or stops a mate.
  2. Work out its line of action: which squares lie between it and the target.
  3. Find your piece that can be put on one of these squares, ideally with tempo (a check, a capture, a threat).
  4. Make sure that capturing the blocking piece does not give back the opponent's original defense.

Tips to spot the idea faster

For kids

Imagine the beam of a flashlight. If you put your hand in the way of the beam, the light will not reach the wall. In the same way, an enemy piece "shines" on what it protects along a straight line, and you put your "hand" (your piece) in the way, and the connection is cut.

The main thing is to place your "hand" so that it is not knocked away right away.

For adults

Look for long diagonals and open files on the board: this is where interference has the biggest effect, because one piece controls many squares at once.

The best blockers are the knight (it jumps "over" pieces) and the pawn (it is cheap and often protected by other pawns).

Examples

Try it yourself: make a move on the board. If you get stuck, press "Show solution".

1. The knight blocks the diagonal: the queen no longer stops the mate

Idea: the black queen on a4 guards the e8 square against a rook mate along the a4 - e8 diagonal. If this diagonal is blocked, the defense disappears.

1.Nd7! - the knight steps onto the a4 - e8 diagonal. The queen no longer sees e8, and 2.Re8# is threatened: mate on the eighth rank (Black cannot make an escape square, because the bishops control h7 and g7). The knight can only be taken at the cost of the queen: 1...Qxd7 2.Bxd7.

Solution: 2.Bxd7 - the queen is given up for the knight: interference backed by the bishop left Black no choice.

2. A pawn blocks the bishop's diagonal

Idea: the black bishop on b7 attacks the white knight on e4 along the b7 - h1 diagonal. The knight can be saved by blocking this diagonal, and with tempo too.

1.c6! - the pawn steps onto the bishop's diagonal and attacks it. If 1...Bxc6, then 2.bxc6: the pawn on b5 protects c6, and White wins the bishop for a pawn. So the bishop has to retreat, and the knight is saved.

Solution: 1.c6! - the pawn blocked the b7 - e4 diagonal and attacks the bishop itself. On 1...Bxc6 comes 2.bxc6, so the bishop will retreat, and the knight is saved.

3. The knight blocks the rook's file and gives check at the same time

Idea: the g7 pawn is attacked by the queen on a7 and the bishop on b2, but the black rook on g2 protects it along the g-file: 1.Qxg7+ right away does not work because of 1...Rxg7. The knight on f8 can block this file with tempo by playing Ng6+.

After 1.Ng6+ the rook loses its connection to the g7 square. On 1...hxg6 or 1...Kg8 comes 2.Qxg7#, and on 1...Rxg6 comes 2.Qa8#: the knight has also cleared the eighth rank. Interference with check is the strongest form of this tactic.

Solution: 2.Qxg7# - the rook on g2 no longer protects g7, and the queen is supported by the bishop on b2.