Editing Backgammon (section)

== Rules ==

[[Image:BackgammonBoard.svg|thumb|250px|Backgammon board in starting position with two dice and a doubling cube]]
[[Image:Bg-movement.svg|thumb|Paths of movement for red and black, with checkers in the starting position; viewed from the black side, with home or inner board at lower right]]
Since 2018, backgammon has been overseen internationally by the [[World Backgammon Federation]] who set the rules of play for international tournaments.

Backgammon playing pieces may be termed men, checkers, draughts, stones, counters, pawns, discs, pips, chips, or nips.<ref>{{cite book |last=Bray |first=Chris |title=Backgammon For Dummies |url=https://books.google.com/books?id=0SoloeOOtSkC&pg=PP23 |date=14 February 2011 |page=23 |publisher=John Wiley & Sons |isbn=9781119996743}}</ref><ref>{{cite book |last=Sfetcu |first=Nicolae |url=https://books.google.com/books?id=sfZ6DQAAQBAJ&pg=PT39 |title=Gaming Guide - Gambling in Europe |date=9 November 2016 |page=39}}</ref> Checkers is a relatively modern American English term derived from another board game, [[draughts]], which in US English is called [[checkers]].

The objective is for players to [[bear off]] all their disc pieces from the board before their opponent can do the same. 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.

=== Board ===

The dimensions of a board when opened, for a tournament game, should be at a minimum of 44&nbsp;cm by 55&nbsp;cm to a maximum of 66&nbsp;cm by 88&nbsp;cm.<ref>{{Cite web|url=https://wbgf.info/tournaments/rules|title = Rules &#124; WBGF}}</ref>

=== Setup ===

Each side of the board has a track of 12 [[isosceles triangle]]s, called [[point (tables game)|points]]. The points form a continuous track in the shape of a horseshoe, and are numbered from 1 to 24. In the most commonly used setup, each player begins with fifteen pieces; two are placed on their 24-point, three on their 8-point, and five each on their 13-point and their 6-point. The two players move their pieces in opposing directions, from the 24-point towards the 1-point.<ref name="robertie-winners">{{cite book|last=Robertie|first=Bill|author-link=Bill Robertie|title=Backgammon for Winners|edition=Third|year=2002|publisher=Cardoza|isbn=978-1-58042-043-3}}</ref>

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 midpoint. The 5-point for each player is sometimes called the "golden point".<ref name="robertie-winners"/><ref name="hoyle">{{cite book|title=Hoyle's Rules of Games|url=https://archive.org/details/hoylesruleso8fav00hoyl|url-access=registration|edition=Third Revised and Updated|publisher=Signet|year=2001|pages=321–330|isbn=978-0-451-20484-4|editor1-first=Albert H.|editor1-last=Morehead|editor2-first=Geoffrey|editor2-last=Mott-Smith|editor-link1=Albert Morehead|editor-link2=Geoffrey Mott-Smith}}</ref>

=== Movement ===

[[File:Backgammon example.ogv|thumb|250px|Video of a backgammon game, showing movement around the board, entering from the bar, formation of primes, use of the doubling cube and bearing off]]
To start the game, each player rolls one die, and the player with the higher number moves first using the numbers shown on both dice. If the players roll the same number, they must roll again until they roll different numbers.<ref>{{cite web|title=Rules of Backgammon|publisher=Backgammon Galore!|url=https://www.bkgm.com/rules.html|quote=To start the game, each player throws a single die. This determines both the player to go first and the numbers to be played.}}</ref>   Both dice must land completely flat on the right-hand side of the gameboard. The players then take alternate turns, rolling two dice at the beginning of each turn.<ref name="robertie-winners"/><ref name="hoyle"/>

After rolling the dice, players must, if possible, move their pieces according to the number shown on each die. For example, if the player rolls a 6 and a 3 (denoted as "6-3"), the player must move one checker six points forward, and another or the same checker three points forward. The same checker may be moved twice, as long as the two moves can be made separately and legally: six and then three, or three and then six. If a player rolls two of the same number, called doubles, that player must play each die twice. For example, a roll of 5-5 allows the player to make four moves of five spaces each. On any roll, a player must move according to the numbers on both dice if it is at all possible to do so. If one or both numbers do not allow a legal move, the player forfeits that portion of the roll and the turn ends. If moves can be made according to either one die or the other, but not both, the higher number must be used. If one die is unable to be moved, but such a move is made possible by the moving of the other die, that move is compulsory.

In the course of a move, a checker may land on any point that is unoccupied or is occupied by one or more of the player's own checkers. It may also land on a point occupied by exactly one opposing checker, or "[[blot (tables game)|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.<ref name="robertie-winners"/><ref name="hoyle"/> There is no limit to the number of checkers that can occupy a point or the bar at any given time.

Checkers placed on the bar must re-enter the game through the opponent's home board before any other move can be made. A roll of 1 allows the checker to enter on the 24-point (opponent's 1), a roll of 2 on the 23-point (opponent's 2), and so forth, up to a roll of 6 allowing entry on the 19-point (opponent's 6). Checkers may not enter on a point occupied by two or more opposing checkers. Checkers can enter on unoccupied points, or on points occupied by a single opposing checker; in the latter case, the single checker is hit and placed on the bar. A player may not move any other checkers until all checkers belonging to that player on the bar have re-entered the board.<ref name="robertie-winners"/><ref name="hoyle"/> If a player has checkers on the bar, but rolls a combination that does not allow any of those checkers to re-enter, the player does not move. If the opponent's home board is completely "closed" (i.e. all six points are each occupied by two or more checkers), there is no roll that will allow a player to enter a checker from the bar, and that player stops rolling and playing until at least one point becomes open (occupied by one or zero checkers) due to the opponent's moves.

A turn ends only when the player has removed his or her dice from the board. Prior to this moment, a move can be undone and replayed an unlimited number of times.

=== Bearing off ===

When all of a player's checkers are in that 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. If all of a player's checkers are on points lower than the number showing on a particular die, the player must use that die to bear off one checker from the highest occupied point.<ref name="robertie-winners"/><ref name="hoyle"/> For example, if a player rolls a 6 and a 5, but has no checkers on the 6-point and two on the 5-point, then the 6 and the 5 must be used to bear off the two 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. For example, if a player has exactly one checker remaining on the 6-point, and rolls a 6 and a 1, the player may move the 6-point checker one place to the 5-point with the lower die roll of 1, and then bear that checker off the 5-point using the die roll of 6; this is sometimes useful tactically. As before, if there is a way to use all moves showing on the dice by moving checkers within the home board or by bearing them off, the player must do so. If a player's checker is hit while in the process of bearing off, that player may not bear off any others until it has been re-entered into the game and moved into the player's home board, according to the normal movement rules.

The first player to bear off all fifteen of their own checkers wins the game. When keeping score in backgammon, the points awarded depend on the scale of the victory.  A player who bears off all fifteen pieces when the opponent has borne off at least one, wins a ''single game'' worth 1 point. If all fifteen have been borne off before the opponent gets at least one checker off, this is a ''gammon'' or ''double game'' worth 2 points. A ''backgammon'' or ''triple game'' is worth 3 points and occurs when the losing player has borne off no pieces and has one or more on the bar and/or in the winner's home table (inner board).<ref name="robertie-winners"/><ref name="hoyle"/>

=== Doubling cube ===

[[Image:Backgammon DoublingCube.jpg|120px|thumb|Doubling cube]]
To speed up match play and to provide an added dimension for strategy, a doubling cube is usually used. The doubling cube is not a die to be rolled, but rather a marker, with the numbers 2, 4, 8, 16, 32, and 64 inscribed on its sides to denote the current stake. At the start of each game, the doubling cube is placed on the midpoint of the bar with the number 64 showing; the cube is then said to be "centered, on 1". When the cube is still centered, either player may start their turn by proposing that the game be played for twice the current stakes. Their opponent must either accept ("take") the doubled stakes or resign ("drop") the game immediately.

Whenever a player accepts doubled stakes, the cube is placed on their side of the board with the corresponding power of two facing upward, to indicate that the right to redouble, which is to offer to continue doubling the stakes, belongs exclusively to that player.<ref name="robertie-winners"/><ref name="hoyle"/> If the opponent drops the doubled stakes, they lose the game at the current value of the doubling cube. For instance, if the cube showed the number 2 and a player wanted to redouble the stakes to put it at 4, the opponent choosing to drop the redouble would lose two, or twice the original stake.

There is no limit on the number of redoubles. 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.<ref name="bill_robertie-beavers">{{cite web|url=http://www.gammonvillage.com/backgammon/news/early_beavers.cfm|title=Backgammon Beavers|access-date=2007-10-17|last=Robertie|first=Bill|publisher=GammonVillage}}</ref>

A variant of the doubling cube "beaver" is the "raccoon". Players who doubled their opponent, seeing the opponent beaver the cube, may in turn then double the stakes once again ("raccoon") as part of that cube phase before any dice are rolled. The opponent retains the doubling cube. An example of a "raccoon" is the following: White doubles Black to 2 points, Black accepts then beavers the cube to 4 points; White, confident of a win, raccoons the cube to 8 points, while Black retains the cube. Such a move adds greatly to the risk of having to face the doubling cube coming back at 8 times its original value when first doubling the opponent (offered at 2 points, counter offered at 16 points) should the luck of the dice change.

Some players may opt to invoke the "Murphy rule" or the "automatic double rule". If both opponents roll the same opening number, the doubling cube is incremented on each occasion yet remains in the middle of the board, available to either player. The Murphy rule may be invoked with a maximum number of automatic doubles allowed and that limit is agreed to prior to a game or match commencing. When a player decides to double the opponent, the value is then a double of whatever face value is shown (e.g. if two automatic doubles have occurred putting the cube up to 4, the first in-game double will be for 8 points). The Murphy rule is not an official rule in backgammon and is rarely, if ever, seen in use at officially sanctioned tournaments.

The "Jacoby rule", named after [[Oswald Jacoby]], 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.<ref name="robertie-serious">{{cite book|last=Robertie|first=Bill|author-link=Bill Robertie|title=Backgammon for Serious Players|edition=second|year=2006|pages=19–22|publisher=Cardoza|isbn=978-0-940685-68-0}}</ref>

The "Crawford rule", named after [[John R. Crawford]], 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 routinely used in tournament match play.<ref name="robertie-serious"/> It is possible for a Crawford game to never occur in a match.

If the Crawford rule is in effect, then another option is the "Holland rule", named after [[Tim Holland (backgammon)|Tim Holland]], which stipulates that after the Crawford game, a player cannot double until after at least two rolls have been played by each side. It was common in tournament play in the 1980s, but is now rarely used.<ref>{{cite web|url=http://www.bkgm.com/gloss/lookup.cgi?pat=holland+rule|title=Backgammon Glossary/Holland Rule|publisher=Backgammon Galore!|access-date=2009-02-26|archive-url=https://web.archive.org/web/20160312074549/http://bkgm.com/gloss/lookup.cgi?pat=holland+rule|archive-date=2016-03-12|url-status=dead}}</ref>