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Blocking and Interception

Blocking places a piece between an attacker and its target. Interception cuts a line that defends a piece.

Blocking a check with a bishop

The rook on e8 gives check to the king on e1 along the file. The bishop moves from d1 to e2 and blocks the file. The check is stopped.

FEN: k3r3/8/8/8/8/8/8/3BK3 w - - 0 1

a b c d e f g h
8 k . . . r . . . 8
7 . . . . . . . . 7
6 . . . . . . . . 6
5 . . . . . . . . 5
4 . . . . . . . . 4
3 . . . . . . . . 3
2 . . . . . . . . 2
1 . . . B K . . . 1
  a b c d e f g h

Blocking an attack on a rook

The queen on a5 attacks the rook on a1 along the file. The pawn moves from a2 to a3 and blocks the file. The rook is no longer attacked.

FEN: 4k3/8/8/q7/8/8/P7/R5K1 w - - 0 1

a b c d e f g h
8 . . . . k . . . 8
7 . . . . . . . . 7
6 . . . . . . . . 6
5 q . . . . . . . 5
4 . . . . . . . . 4
3 . . . . . . . . 3
2 P . . . . . . . 2
1 R . . . . . K . 1
  a b c d e f g h

Key points

  • A block stops a check along a rank, file, or diagonal.
  • A block stops an attack on a valuable piece.
  • The blocking piece must be able to reach the line.
  • A block works only against a line piece, not a knight.
  • Interception blocks a defender's line to the piece it guards.
  • After interception, the guarded piece can be captured.
  • A block or interception often gains a move, because the threat must be answered.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Rust Playground

Exercise

White to move, in check from the rook on a8. Which move blocks the check?