A trapped piece is a piece with no safe square to escape to. Once attacked, it is lost — regardless of how valuable it is or how 'active' it looked a move ago. Pieces most often get trapped chasing pawns deep in enemy territory.
Material in chess is only worth what its mobility allows. A trapped piece is the purest demonstration: a full bishop or rook, alive on the board, functionally already captured — the opponent just hasn't collected yet.
The classic: White's bishop captures a pawn on a7, deep in Black's queenside. Black calmly replies b6. Look at the bishop's world now — the b8 square is covered, the b6 pawn blocks the diagonal home, and there is no third exit. Black plays a rook to a8 or simply walks the king over, and the bishop is collected at leisure. White won a pawn and lost a bishop; the pawn on a7 was poisoned.
Every experienced player has a version of this scar. Greedy grabs on b2/g2/b7/g7 with the queen are the same story with higher stakes — the queen that eats the b2 pawn and never comes home is practically a rite of passage.
Three ingredients recur. Depth: pieces in enemy territory have fewer retreat squares by geometry. Pawn walls: pawns are the cheapest jailers — they cover escape squares without risking anything of value. Tempo: a piece that must run is a piece the opponent develops against for free; sometimes the chase alone wins the game even if the piece escapes.
Before sending any piece past the fourth rank to win material, run the exit check: after the capture, list the squares it can legally reach next move, and ask which of them the opponent can cover in one move. If the answer is 'all of them', the material isn't free — it's bait. This is the same discipline as checking a capture for a zwischenzug: forcing sequences deserve one extra beat of scepticism.
The hunt works in reverse, too. When an enemy piece ventures deep, don't panic about what it attacks — count its exits. Spending a quiet pawn move to seal the last one is often worth more than any direct threat, and engines flag these opportunities constantly in game analysis.
Chessdock catches both sides of the pattern in your own play — the pieces you got trapped and the trapping chances you walked past — and turns them into puzzles from your real positions.