Tactics: Interference

In chess, interference involves interrupting the line between 2 pieces by inserting (interposing) a piece. The inserted piece must itself represent a threat. Some chess authorities insist that interference requires a sacrifice, but this is not always the case. Moreover the value of the interposed piece is irrelevant if it is not sacrificed for greater material. 

• Almost every piece is capable of interference except the king. In extremely rare circumstances the queen may even be interposed.

The purpose of a successful Interference Tactic is to:

1. Gain a material advantage.

2. Upset your opponent's defenses.

3. Set up a checkmating opportunity.

Below are several diagrams 
illustrating the overloading tactic.

A green colored box represents the interposing/attacking piece
A blue colored box represents the path of attack
A red colored box represents the target(s) of the attack
A purple colored box represents the line interfered with

Diagram 1.1

(Black to move)

White's E2 bishop is pinned and the only 

thing stopping checkmate is white's A6 queen

Diagram 1.2

(Black's bishop interferes with 
white's queenly protection of white's bishop)

If white captures black's B5 bishop with its queen, the queen 

is lost the following turn. If it captures the bishop with its 

A4 pawn then black can proceed with checkmate