Undefended chess term

Undefended

Definition

In chess a piece or pawn is undefended (also called “loose” or “unprotected”) when no friendly unit—king included—currently guards the square it occupies. Because a single legal capture removes it from the board without immediate recapture, an undefended man is a potential tactical target.

How the term is used

Players, engines, and authors routinely mark an undefended piece with an “LP” (Loose Piece) or a red highlight in diagrams. Typical contexts:

• Counting defenders vs. attackers. “The knight on c6 is attacked twice and defended once; after 1. d5 it becomes undefended.”
• Forming tactical motifs. Double attacks, pins, skewers, discoveries, and forks often work because a target is undefended and therefore cannot be exchanged favorably.
• Evaluation heuristics. Engine score sheets sometimes list “Loose Pieces Drop Off” (LPDO), a phrase made famous by GM Yasser Seirawan.

Strategic significance

Keeping your own pieces defended while locating your opponent’s undefended units is a cornerstone of prophylaxis. An undefended piece need not be attacked to be a liability; once a forcing line starts, it may be impossible to protect it in time. Conversely, deliberately leaving a piece undefended can be a form of zwischenzug bait, tempting an opponent into an unsound capture.

Illustrative positions

1. Elementary fork.

   After 5…Nxd5?? Black’s knight on d5 lands on a square that no black piece protects; White replies 6. Nxf7, forking the queen and rook. The tactic succeeds because the knight on d5 was undefended.

2. “Game of the Century” – Fischer vs Byrne, New York 1956.

   Fischer’s stunning 17…Be6!! left his queen apparently hanging. When Byrne accepted the offer, multiple Byrne pieces became simultaneously undefended; Fischer’s follow-up 19…Bxc4+ and 20…Qc3+ swept them away. The combination is still replayed in tactics books to show how undefended pieces amplify the power of checks and discoveries.

3. World Championship anecdote.

   In Kasparov – Anand (WCh 1995, game 10) Kasparov exploited an undefended rook on c8 with the exchange sacrifice 16.Rxc8! Rxc8 17.Qg4, tying Anand’s forces to defense and preparing a kingside storm. Even top-level players are forced onto the back foot when a major piece is left loose.

Historical notes & trivia

• The phrase LPDO – Loose Pieces Drop Off was coined on air by GM Yasser Seirawan during a 1990s broadcast; it quickly entered the chess lexicon.
• In 18th-century manuscripts the adjective “naked” was sometimes used in place of “undefended.” Philidor warned that “a naked piece is a prisoner waiting parole.”
• Modern engines assign a material-weighted penalty to every undefended unit in their evaluation function—part of why beginner positions are often scored as lost long before checkmate is visible.

Key take-aways

• Before launching an attack, ask “What is still undefended?” on both sides of the board.
• If you must leave something loose, ensure you create counter-threats so big that the opponent has no time to take it.
• Spotting undefended pieces is one of the fastest ways to improve tactical vision—set a 3-second “LPDO scan” after every opponent move.