Castling short looks like the most dangerous move in chess, and the truth is stranger: it is a trick of how we write moves down. O-O is the one move with a symbol of its own, while every knight move is split across a dozen spellings, so castling wins a count it was never really in. Group blunders by the PIECE that moved instead and castling is the smallest category there is.

Castling short looks like the most dangerous move in chess, and the truth is stranger: it is a trick of how we write moves down.

O-O is the one move with a symbol of its own, while every knight move is split across a dozen spellings, so castling wins a count it was never really in. Group blunders by the PIECE that moved instead and castling is the smallest category there is.

O-O tops the list for 61 of 244 players and is about 1.0% of any one player's blunders, measured across 307,650 games containing a move that cost at least 300 centipawns. Read it as a fact about counting, not as advice: newsroom_corpus_worst_piece() puts castling at 1.4% of blunders against the queen's 19.8%.

Across 307,650 analysed games from 244 players.

The Club Ledger · No. 7

The later you blunder, the more it costs you.

A player's worst move is worth about four and a half pawns in the opening stretch of a game. By the closing stretch of the same game it is worth about eight pawns, a rook and a bishop instead.

Walk a game from start to finish in five stages and the damage climbs at every one: about four and a half pawns in the opening stretch, then more, then more again, until the last fifth costs about eight pawns, a rook and a bishop. It is not simply that long games contain more mistakes. The same mistake is worth more when it arrives late, because by then there is less position left to recover in and usually less clock to find the recovery with.

Across 361,055 analysed games from 246 players.

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