Chess is a two-player board game using a chessboard and sixteen pieces of six types for each player. Each type of piece moves in a distinct way. The object of the game is to checkmate (threaten with inescapable capture) the opponent's king. Games do not necessarily end in checkmate; players often resign if they believe they will lose. A game can also end in a draw in several ways.
Chess is played on a chessboard, a square board divided into 64 squares (eight-by-eight) of alternating color. Sixteen "white" and sixteen "black" pieces are placed on the board at the beginning of the game. The board is placed so that a white square is in each player's near-right corner. Horizontal rows are called ranks and vertical rows are called files.
Each player controls sixteen pieces. At the beginning of the game, the pieces are arranged as shown in the diagram: for each side one king, one queen, two rooks, two bishops, two knights, and eight pawns.
The player controlling the white pieces is named "White"; the player controlling the black pieces is named "Black". White moves first, then players alternate moves. Making a move is required; it is not legal to skip a move, even when having to move is detrimental. Play continues until a king is checkmated, a player resigns, or a draw is declared, as explained below. In addition, if the game is being played under a time control players who exceed their time limit lose the game.
Each type of chess piece has its own method of movement. A piece moves to a vacant square except when capturing an opponent's piece.
Except for any move of the knight and castling, pieces cannot jump over other pieces. A piece is captured (or taken) when an attacking enemy piece replaces it on its square (en passant is the only exception). The captured piece is thereby permanently removed from the game. The king can be put in check but cannot be captured (see below).
- The king moves exactly one square horizontally, vertically, or diagonally. A special move with the king known as castling is allowed only once per player, per game (see below).
- A rook moves any number of vacant squares horizontally or vertically. It also is moved when castling.
- A bishop moves any number of vacant squares diagonally.
- The queen moves any number of vacant squares horizontally, vertically, or diagonally.
- A knight moves to the nearest square not on the same rank, file, or diagonal. (This can be thought of as moving two squares horizontally then one square vertically, or moving one square horizontally then two squares vertically—i.e. in an "L" pattern.) The knight is not blocked by other pieces: it jumps to the new location.
- Pawns have the most complex rules of movement:
- A pawn moves straight forward one square, if that square is vacant. If it has not yet moved, a pawn also has the option of moving two squares straight forward, provided both squares are vacant. Pawns cannot move backwards.Pawns are the only pieces that capture differently from how they move. A pawn can capture an enemy piece on either of the two squares diagonally in front of the pawn (but cannot move to those squares if they are vacant). The pawn is also involved in the two special moves en passant and promotion.
Castling consists of moving the king two squares towards a rook, then placing the rook on the other side of the king, adjacent to it. It is not allowed to move both king and rook in the same time, because "Each move must be played with one hand only. Castling is only permissible if all of the following conditions hold:
- The king and rook involved in castling must not have previously moved;
- There must be no pieces between the king and the rook;
- The king may not currently be in check, nor may the king pass through or end up in a square that is under attack by an enemy piece (though the rook is permitted to be under attack and to pass over an attacked square);
- The castling must be kingside or queenside as shown in the diagram.
When a pawn advances two squares from its original square and ends the turn adjacent to a pawn of the opponent's on the same rank, it may be captured by that pawn of the opponent's, as if it had moved only one square forward. This capture is only legal on the opponent's next move immediately following the first pawn's advance.
If a player advances a pawn to its eighth rank, the pawn is then promoted (converted) to a queen, rook, bishop, or knight of the same color at the choice of the player (a queen is usually chosen). The choice is not limited to previously captured pieces. Hence it is theoretically possible for a player to have up to nine queens or up to ten rooks, bishops, or knights if all of their pawns are promoted. If the desired piece is not available, the player must call the arbiter to provide the piece.
A king is in check when it is under attack by at least one enemy piece. A piece unable to move because it would place its own king in check (it is pinned against its own king) may still deliver check to the opposing player.
It is illegal to make a move that places or leaves one's king in check. The possible ways to get out of check are:
- Move the king to a square where it is not in check.
- Capture the checking piece (possibly with the king).
- Block the check by placing a piece between the king and the opponent's threatening piece.
If it is not possible to get out of check, the king is checkmated and the game is over. In informal games, it is customary to announce "check" when making a move that puts the opponent's king in check. However, in formal competitions check is rarely announced.
If a player's king is placed in check and there is no legal move that player can make to escape check, then the king is said to be checkmated, the game ends, and that player loses. Unlike other pieces, capturing the opponent's king is not allowed.
More information and reference: Wikipedia