Chess tactics
What Is Interference in Chess?
Interference is a tactic in which you place a piece on the line between an enemy defender and the square or piece it protects. The defender is cut off, so the target loses its protection even though the defender never moved.
Example
1. Rc8 Rxc8 2. dxc8=Q
The rook on a8 stops the pawn by guarding d8 along the back rank. Rc8 puts a piece in the way. If Rxc8, the pawn takes back and promotes with dxc8=Q, and any other rook move allows d8=Q.
How interference works
Bishops, rooks, and queens defend along lines. If you put a piece on one of the squares in between, the line is blocked and the defense stops working. The interfering piece is often offered as a sacrifice, but capturing it either costs the defender or still leaves the target unprotected.
In the example, capturing the rook on c8 moves the black rook onto a square the pawn can capture with promotion. Leaving it alone means the rook no longer sees d8. Either way the pawn queens.
Where it shows up
Promotion races are the most common setting: a rook or bishop guards the queening square, and a piece dropped on its line breaks the guard. Back-rank mates are another, when a defender covers the mating square from a distance.
Interference can also be a pawn push that cuts a bishop's diagonal, with the pawn defended so that capturing it costs the bishop.
How to spot it
When a target is defended from a distance, trace the line from defender to target and look at the empty squares on it. Ask whether any of your pieces can land there, ideally with check or with a second threat.
Common questions
What is the difference between interference and removing the defender?
Removing the defender gets rid of the guard by capturing or chasing it. Interference leaves the guard where it is but blocks its line, so it can no longer reach the target.
Is interference the same as blocking?
It is a kind of blocking, used to attack. A defensive block stops an attack on your own pieces, while interference blocks an enemy defender's line so your attack succeeds.
What is a Novotny interference?
It is a special case from chess problems: a piece is placed on the square where the lines of an enemy rook and an enemy bishop cross. Whichever piece captures it blocks the other one's line.
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