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Trapping a Piece

Trapping a piece means cutting off all its escape squares. The trapped piece is then captured for free.

A knight trapped by pawns

The knight on a5 has no safe escape. The pawn on a6 attacks b7, the pawn on b7 attacks c6, the pawn on b5 attacks c4, and the pawn on a4 attacks b3. The pawn on b6 captures the knight.

FEN: 4k3/1pp5/pp6/NP6/p7/8/8/6K1 b - - 0 1

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

A bishop trapped by pawns

The black bishop on a7 has no safe escape. The pawn on c7 attacks b8, and the pawn on b6 stands on the other escape square, defended by the pawn on a5. The pawn on b6 captures the bishop.

FEN: 4k3/b1P5/1P6/P7/8/8/8/6K1 w - - 0 1

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

Key points

  • A trapped piece has no safe square to move to.
  • Pawns are the usual trappers, because they attack many squares cheaply.
  • A piece on the edge of the board is easier to trap.
  • A piece deep in enemy territory is easier to trap.
  • Trap a piece by attacking its escape squares one by one.
  • A trapped piece can sometimes sacrifice itself for a pawn.
  • Check every escape square before you call a piece trapped.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Rust Playground

Exercise

Black to move. Which move captures the trapped knight on a5?