Line clearance

Line clearance is a specific form of clearance. A friendly piece leaves a vertical file, a horizontal rank, or a diagonal so that a rook, bishop, or queen can operate along it. The purpose is not merely to improve the moving piece, but to free the path of the piece behind it.

The blocker may retreat, make a capture, or move to a square where it will be captured. The strongest clearing moves gain time by giving check, directly attacking the king, attacking a piece, or creating a threat that prevents the opponent from reorganizing. When the blocker is deliberately given up, the move may also be a vacating sacrifice.

Not every opened line is classified primarily as line clearance. For example, a pawn break, a pawn move intended to change or open the pawn arrangement, may also open a file. The defining feature of line clearance is that a friendly piece was the obstacle and moves to release another friendly piece; one move may carry both labels. Nor is it identical to a discovered attack: line clearance names the purpose of opening the route, while discovered attack names the attack revealed by doing so.