Rules
Paths of movement for red and black, with checkers in the starting position
The objective of backgammon is to move all of one’s own checkers past those of one’s opponent and then remove them from the board. The checkers are scattered at first and may be blocked or hit by the opponent. As the playing time for each individual game is short, it is often played in matches, where victory is awarded to the first player to reach a certain number of points.
Setup
Each side of the board has a track of 12 long triangles, called points. The points are considered to be connected across one edge of the board, forming a continuous track in the shape of a horseshoe, and are numbered from 1 to 24. Each player begins with two checkers on his 24-point, three checkers on his 8-point, and five checkers each on his 13-point and his 6-point. The two players move their checkers in opposing directions, each from his own 24-point towards his 1-point.
Points 1 through 6 are called the home board or inner board, and points 7 through 12 are called the outer board. The 7-point is referred to as the bar point, and the 13-point as the mid point.
Movement
To start the game, each player rolls one die, and the player with the higher number moves first using the numbers shown. Both dice must land completely flat on the right hand side of the gameboard. The players then alternate turns, rolling two dice at the beginning of each turn.
After rolling the dice a player must, if possible, move his checkers according to the number of pips shown on each die. For example, if the player rolls a 6 and a 3 (noted as “6-3″), that player must move one checker six points forward, and another checker three points forward. The same checker may be moved twice as long as the two moves are distinct: six and then three, or three and then six, but not all nine at once. If a player rolls two of the same number, called doubles, that player must play each die twice. For example, upon rolling a 5-5 that player must move four checkers forward five spaces each.
In the course of a move, a checker may land on any point that is unoccupied or is occupied only by a player’s own checkers. It may also land on a point occupied by exactly one opposing checker; such a lone piece is called a blot. In this case, the blot has been hit, and is placed in the middle of the board on the bar that divides the two sides of the playing surface. A checker may never land on a point occupied by two or more opposing checkers; thus, no point is ever occupied by checkers from both players simultaneously.
Checkers placed on the bar re-enter the game through the hitting player’s home board. A roll of 2 allows the checker to enter on the 23-point, a roll of 3 on the 22-point, and so forth. A player may not move any other checkers until all checkers on the bar belonging to that player have re-entered the game.
When all of a player’s checkers are in the player’s home board, that player may start removing them; this is called bearing off. A roll of 1 may be used to bear off a checker from the 1-point, a 2 from the 2-point, and so on. A die may not be used to bear off checkers from a lower-numbered point unless there are no checkers on any higher points. For example if a player rolls a 6 and a 5, but has no checkers on the 6-point, though 2 checkers remain on the 5-point, then the 6 and the 5 must be used to bear off the 2 checkers from the 5-point. When bearing off, a player may also move a lower die roll before the higher even if that means ‘the full value of the higher die’ is not fully utilized. In other words if a player has exactly 1 checker remaining on the 6-point, and rolls a 6 and a 1, the player may move the 6-point checker 1 place to the 5-point with the lower die roll of 1, and then bear that piece off the 5-point using the die roll of 6, this is sometimes useful tactically.
If one player has not borne off any checkers by the time that player’s opponent has borne off all fifteen, then the player has lost a gammon, which counts for double a normal loss. If the losing player still has checkers on the bar or in the opponent’s home board, then the player has lost a backgammon, which counts for triple a normal loss.
Doubling cube
To speed up match play and to provide an added dimension for strategy and betting, a doubling cube is normally used. The doubling cube is a six-sided die marked with the numbers 2, 4, 8, 16, 32, and 64. Before rolling the dice on his turn, a player may demand that the game be played for twice the current stakes. His opponent must either accept the new stakes or resign the game immediately. Thereafter, the right to redouble belongs exclusively to the player who last accepted a double. Whenever a player accepts doubled stakes, the cube is placed with the corresponding power of two facing upward.
The game is rarely redoubled beyond four times the original stake, but there is no limit on the number of doubles. Although 64 is the highest number depicted on the doubling cube, the stakes may rise to 128, 256, and so on. In money games, a player is often permitted to “beaver” when offered the cube, doubling the value of the game again, while retaining possession of the cube.
The Jacoby rule allows gammons and backgammons to count for their respective double and triple values only if the cube has already been offered and accepted. This encourages a player with a large lead to double, possibly ending the game, rather than to play it to conclusion hoping for a gammon or backgammon. The Jacoby rule is widely used in money play but is not used in match play.
The Crawford rule is designed to make match play more equitable for the player in the lead. If a player is one point away from winning a match, that player’s opponent will always want to double as early as possible in order to catch up. Whether the game is worth one point or two, the trailing player must win to continue the match. To balance the situation, the Crawford rule requires that when a player first reaches a score one point short of winning, neither player may use the doubling cube for the following game, called the Crawford game. After the Crawford game, normal use of the doubling cube resumes. The Crawford rule is used in tournament match play.
Variants
Todas tablas from the Libro de los juegos
There are many variants of standard backgammon rules. Some are played primarily throughout one geographic region, and others add new tactical elements to the game. Variants commonly alter the starting position, restrict certain moves, or assign special value to certain dice rolls.
A common variant is to only allow a maximum of five checkers on any point. This variation is not part of the official rules, but has proved popular with casual players in some regions . The popular GNU Backgammon software has an option for this, which is described as the ‘Egyptian Rule’, however the origin of that name might be due to a humorous invention.
Acey-deucey is a variant of backgammon in which players start with no checkers on the board, and must bear them on at the beginning of the game. The roll of 1-2 is given special consideration, allowing the player to select doubles of his choice. A player also receives an extra turn after a roll of 1-2 or of doubles.
Hypergammon is a variant of backgammon in which players have only three checkers on the board, starting with one each on the 24-, 23- and 22-points. The game has been strongly solved, meaning that exact equities are available for all 32 million possible positions.
Nackgammon is a variant of backgammon invented by Nack Ballard in which players start with one fewer checker on the six point and midpoint and two checkers on the 23 point.
From Wikipedia “Backgammon”
http://en.wikipedia.org/w/index.php?title=Backgammon&oldid=187539127
Licensed under the GNUFDL,
http://en.wikipedia.org/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License
Backgammon has an established opening theory, although it is less detailed than that of games like chess. The tree of positions expands rapidly because of the number of possible dice rolls and the moves available on each turn. Recent computer analysis has offered more insight on opening plays, but the midgame is reached quickly. After the opening, backgammon players frequently rely on some established general strategies, combining and switching among them to adapt to the changing conditions of a game.The most direct strategy is simply to avoid being hit, trapped, or held in a stand-off. A “running game” describes a strategy of moving as quickly as possible around the board, and is most successful when a player is already ahead in the race. When this fails, one may opt for a “holding game”, maintaining control of a point on one’s opponent’s side of the board, called an anchor. As the game progresses, this player may gain an advantage by hitting an opponent’s blot from the anchor, or by rolling large doubles that allow the checkers to escape into a running game.
A backgammon set, consisting of a board, two sets of 15 checkers, two pairs of dice, a doubling cube, and dice cups