Check (board game)
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In games such as chess, shogi, and xiangqi, a check is an immediate threat to capture the king (or general in xiangqi). A king so threatened is said to be in check. In friendly games, it is customary for a player checking the opposing king to warn the opponent by saying "check". In the following move, the player whose king is in check must get his king out of check. Either the threat must be stopped (by interposing a piece between the threatening piece and the king, or capturing the threatening piece) or the king must be moved to a space where it is no longer in check. In chess, if the king is in check and there is no allowable move which gets the king out of check, the king is said to be checkmated and the game is over. The player whose king is checkmated loses and the opposing player, who checkmates the king, wins the game. In this usage, the words "check" and "chess" come via Arabic from Persian shāh = "king".
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[edit] Check in the game of chess
For a king to be checked (placed in check) in a chess game, the opponent makes a checking move so that one (or more) of his pieces attacks the king to be checked. However, it is against the rules for a player to make a move which puts his/her own king in check. The checking piece is the one that is attacking the opposing king, which is often, but not necessarily always, the same piece that was moved in the checking move. A checking move may or may not involve a capture of one of the other player's pieces. In algebraic chess notation, a checking move is noted like any other move, except that a + is written after the move. In friendly games, the checking player customarily says "check" when making a checking move. Less commonly (and essentially obsolete), the warning garde can be said when a player directly attacks the opponent's queen in a similar way. The same move can be both check and garde simultaneously. A king cannot directly check the opposing king himself, since this would place the first king in check. However, a king can still make a checking move by exposing one of his other pieces so that it is attacking the other king. Accordingly, the two opposing kings can never be placed on squares next to each other. Any other type of piece may be able to check the opposing king.
[edit] Types of checks
A simple and very common type of check is when a piece moves to directly attack the opposing king only by itself. Sometimes such a check is part of a chess tactic such as a fork, a skewer, or a discovered attack on another piece. In some cases, a check can be used to defend against such tactics.
There are also a few more special types of check:
- Discovered check - A discovered check is similar to any other type of discovered attack except that it is a discovered attack on the opposing king. In a discovered check, a piece moves out of the line of attack by another piece so that this other piece (which can be a queen, rook, or bishop) is then checking the opponent's king. The piece that actually moved in the discovered check move could possibly be any type of piece belonging to the same player as the checking piece except queen or the same type of piece administering the check. A discovered check could be a tactic in itself because the piece that moved could attack or otherwise create a threat to another piece on the checked king's side. The opponent has to get out of the discovered check on the following move and may not get a chance to thwart the attack by the other piece that moved.
- Double check - A double check is when two pieces check the opponent's king on the same checking move. This happens when the piece that moved during the checking move attacks the king and another piece checks by discovered check on the same move. In algebraic chess notation, a double check move is sometimes noted with a ++ after the written move in place of the usual +, although sometimes ++ has been used to indicate checkmate in more modern literature (see here). When ++ is used to indicate double check, # is used to indicate checkmate, but using ++ for double check is obsolete.
- Cross-check - In chess, when a check is answered by a check, particularly when this second check is delivered by a piece blocking the first, it is termed a cross-check.
[edit] Getting out of check
There may be up to three possible ways to get a king out of a single check on the following move:
- Capturing the checking piece, with either the king or another piece. If the checking piece is on a square next to the king, the king can capture the piece if the king does not move into a new check, i.e. if the piece is not protected by another enemy piece.
- Moving the king to an adjacent square where it will not be in check. The king is not allowed to castle when it is in check. The king may or may not capture an enemy piece in a move to get out of check, as long as the piece is not protected.
- Blocking the check. This will only work if the checking piece is a queen, rook, or bishop and there is at least one empty square in the line between this checking piece and the checked king. Blocking a check is done by moving a piece (from the checked king's army) to a square in line in between the checking piece and the checked king. The blocking piece is then absolutely pinned to the king by the attacking piece (until it is unpinned). This is just one way for a pin to be created; there are others.
If a king is placed in double check, the king must get out both checks on the following move. Since it is impossible to capture both checking pieces or block both lines of attack in a single move, a double check can be escaped only by moving the king out of check. The king may, however, capture one of the checking pieces in the process, if that piece is adjacent to the king and not protected by another piece.
If none of these possibilities can get the king out of check, then it is checkmated and the game is won/lost.
[edit] Checking in tactics and strategy
Checking an opponent in a game of chess does not score any points and sometimes provides no benefit to the checking player. A check useless to the checking player may even provide the checked opponent with a tempo (move opportunity) to move his king into a safer position. However, there are many times when checking the opponent's king may be a useful tactic or part of a tactic, either in attacking or in defense. Checking is often used in combinations with many other tactics or simply to force an opponent into a position where the opposing king can be checkmated, otherwise taken advantage of, or is otherwise worse for the opponent. Some attacks involves numerous checks to force an opponent into a losing position, especially when the king is exposed. An unexpected check in a forced combination or an overlooked cross-check in a planned series of checks may serve as sort of a zwischenzug, foiling the plan.
Some uses of checking:
- Repetitive checking to prevent losing a game going poorly
- Royal fork (knight fork of king and queen) or other forks involving the king
- Checks to force an exchange
- A double check could be especially bad for the opponent since there are likely to be fewer options to get out of check. A double check is often more likely to lead to checkmate or loss of material.
- A check might force a king to move so that it cannot castle later.
- Moving a piece to give check can sometimes open a line of attack on another piece. The opponent must escape the check, and therefore cannot (in general) prevent the other piece from being captured.
- Similarly, the piece moved to create a discovered check may attack another enemy piece, leading to the same scenario.
