{"schema":"chessgrammar_motif_entry/1","slug":"skewer","name":"Skewer","aka":"reverse pin","category":{"key":"motif","label":"Direct tactics"},"edition":{"version":"v3.0","year":"2026"},"certified":true,"canonical":"https://chessgrammar.com/motifs/tactics/skewer","tabs":{"identity":"https://chessgrammar.com/motifs/tactics/skewer#identity","structure":"https://chessgrammar.com/motifs/tactics/skewer#structure","examples":"https://chessgrammar.com/motifs/tactics/skewer#examples"},"citation":"ChessGrammar (2026). Skewer. In: ChessGrammar: A reference for chess concepts, Tactics grammar, edition v3.0. Entry cg:skewer@1. https://chessgrammar.com/motifs/tactics/skewer","variants":["absolute","axial","bishop","diagonal","king_queen","king_rook","queen","queen_rook","relative","rook","with_check"],"seeAlso":["pin","discovered-attack"],"definition":{"id":"cg:skewer@1","statement":"A sliding piece attacks a valuable enemy piece which must move. Moving it exposes a less valuable enemy piece, directly behind it on the same ray, to capture.","predicate":["After the move, three pieces lie in a row on the same rank, file or diagonal. The attacking slider stands at the back. The enemy piece immediately in front of it is the screen. A second enemy piece directly behind the screen on the same line is the target.","The screen is the king, or the screen is worth more than the target. If the screen is worth less than the target, the same three pieces form a Pin. If screen and target are equal in value, neither motif applies.","The move played creates this three-piece alignment, which did not exist before the slider moved. The gain holds against the best defence. The screen must move, and the target then cannot be saved either."],"diagnosis":"Its nearest neighbour is the Pin, the mirror image of the same three-piece line. The three squares and the line are the same. In a Pin, the front piece cannot move or shields the king, and the front piece is the one that stays bound. Which of the two applies depends only on whether the screen outranks the target or is the king. It never depends on which piece is worth more in absolute terms.","maturity":{"state":"stable"},"holotype":{"fen":"r5r1/5k1p/4q1p1/2p2p2/2n5/P1Q1P3/4R1PP/B4RK1 b - - 2 30","move":"a8a3","san":"Rxa3","attacker":"a3","screen":"c3","target":"e3","why":"The black rook captures on a3 and faces the white queen on c3, with the white pawn on e3 lined up behind it on the same rank. The queen must move to safety. Once it does, the pawn falls too against any defence, so the skewer wins material."},"nearMiss":{"fen":"r5r1/5k1p/4q1p1/2p2p2/2n5/P1P1P3/4R1PP/B4RK1 b - - 2 30","move":"a8a3","san":"Rxa3","attacker":"a3","screen":"c3","target":"e3","why":"The screen queen is replaced by a pawn, equal in value to the target pawn behind it on the same rank. The front and back pieces are worth the same, so the position is not a Skewer and not a Pin.","delta":"The screen queen on c3 is replaced by a white pawn, equal in value to the target pawn on e3.","neighbour":"residue","note":"A Pin neighbour (value_order LT) was tried first, per Steve's reco. It is unreachable in one trait: the holotype's screen is already the maximum-value piece (queen) and its target is already the minimum-value piece (pawn), so no single-piece edit can push value_order below EQ -- residue is the closest reachable neighbour."},"nearMissPending":"Earlier pin-shaped neighbour, superseded by the published minimal pair.","standing":{"certified":true,"scope":"definition"}},"axes":[{"key":"screen","name":"The screen piece (front of the ray)","values":["absolute","relative"],"nature":"partition","note":"Absolute: the screening piece is the king, whose flight is a forced check-response, not a choice. Relative: the screening piece is not the king, and ranks above the piece behind it on the same line."},{"key":"direction","name":"The ray's direction","values":["axial","diagonal"],"nature":"partition","note":"Axial: the line runs along a rank or file (rook or queen). Diagonal: the line runs along a diagonal (bishop or queen)."},{"key":"check","name":"Check on the trigger move","values":["with_check"],"nature":"facts","note":"An independent fact: the trigger move gives check, read on the board itself, not on the line."},{"key":"pieces","name":"The piece identities on the ray (screen, or screen-target pair)","values":["king_queen","king_rook","queen_rook","queen","rook","bishop"],"nature":"facts","note":"Reads the types of the screening piece and the target piece off the same line. Pair-named values are declared before simple ones, because the paired queen-rook value implies the plain queen value (same screening-piece type). Unlike the screen and direction axes this is not a partition: a knight screen, or a king screen over a pawn, knight or bishop, carries no value on this axis."}],"summary":"A valuable piece is attacked along a line and must move, which exposes a less valuable piece behind it."}