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Backgammon is a simple game with deep strategic
elements. It does not take long to learn to play, although obscure
situations do arise which require careful interpretation of the
rules. The playing time for each individual game is short, so it is
often played in matches, for example the first to five points. Game
and match are used in Backgammon to refer to these distinct
elements, as in, "I won two games in a row, but then she won three
in a row and I lost the match, three points to two."
In short, players are trying to get all of their pieces past their
opponent's pieces. This is difficult because the pieces are
scattered at first, and may be blocked or captured by the opponent's
pieces.
Each side of the board has a track of twelve adjacent spaces, called
points and usually represented by long triangles of alternating (but
meaningless) color. The tracks are imagined to be connected across
the break in the middle and on just one edge of the board, making a
continuous line (but not a circle) of twenty-four points. The points
are numbered from 1 to 24, with checkers always moving from
higher-numbered points to lower-numbered points. The two players
move their checkers in opposite directions, so the 1-point for one
player is the 24-point for the other. Some recorded games, however,
keep the numbering of the points constant from the perspective of
one player.
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.
Note that the board as shown can be flipped horizontally, with
starting positions and direction of play likewise flipped but with
no changes to the mechanics of gameplay. The two orientations are
equally common and game boards are all designed to be played both
ways.
Points one to six, where the player wants to get his pieces to, are
called the home board or inner board. A player may not bear off any
checkers unless all of his checkers are in his home board. Points
seven to twelve are called the outer board, points thirteen to
eighteen are the opponent's outer board, and points nineteen to
twenty-four are the opponent's home board. The 7-point is often
referred to as the bar point and the 13-point as the mid point.
At the start of the game, each player rolls one die. Whoever rolls
higher starts his first turn using the numbers on the already-rolled
dice. In case of a tie, the players roll again. The players
alternate turns and roll two dice at the beginning of each turn
after the first.
After rolling the dice a player must, if possible, move checkers the
number of points showing on each die. For example, if he rolls a 6
and a 3, he must move one checker six points forward and another one
three points forward. The dice may be played in either order. 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 nine
all at once.
If a player has no legal moves after rolling the dice, because all
of the points to which he might move are occupied by two or more
enemy checkers, he forfeits his turn. However, a player must play
both dice if it is possible. If he has a legal move for one die
only, he must make that move and then forfeit the use of the other
die. (If he has a legal move for either die, but not both, he must
play the higher number.)
If a player rolls two of the same number (doubles) he must play each
die twice. For example, upon rolling a 5 and a 5, he must play four
checkers forward five spaces each. As before, a checker may be moved
multiple times as long as the moves are distinct.
A checker may land on any point occupied by no checkers or by
friendly checkers. Also it may land on a point occupied by exactly
one enemy checker (a lone piece is called a blot). In the latter
case the blot has been hit, and is temporarily placed in the middle
of the board on the bar, i.e., the divider between the home boards
and the outfields. A checker may never land on a point occupied by
two or more enemy checkers. Thus no point is ever occupied by
checkers from both players at the same time.
Checkers on the bar re-enter the game through the opponent's home
field. A roll of 1 allows the checker to enter on the 24-point, a
roll of 2 on the 23-point, etc. A player with one or more checkers
on the bar may not move any other checkers until all of the checkers
on the bar have re-entered the opponent's home field.
When all of a player's checkers are in his home board, he may remove
them from the board, or bear them off. A roll of 1 may be used to
bear off a checker from the 1-point, a 2 from the 2-point, etc. A
number may not be used to bear off checkers from a lower point
unless there are no checkers on any higher points. For example, a 4
may be used to bear off a checker from the 3-point only if there are
no checkers on the 4-, 5-, and 6-points.
A checker borne off from a lower point than indicated on the die
still counts as the full die. For instance, suppose a player has
only one checker on his 2-point and two checkers on his 1-point.
Then on rolling 1-2, he may move the checker from the 2-point to the
1-point (using the 1 rolled), and then bear off from the 1-point
(using the 2 rolled). He is not required to maximize the use of his
rolled 2 by bearing off from the 2-point.
If one player has not borne off any checkers by the time his
opponent has borne off all fifteen, he has lost a gammon, which
counts for twice a normal loss. If a player has not borne off any
checkers, and still has checkers on the bar, or in his opponent's
home board by the time his opponent has borne off all fifteen, or
both, he has lost a backgammon, which counts for triple a normal
loss. Sometimes a distinction is made between pieces in the
opponent's home board (triple loss) and pieces on the bar (quadruple
loss).
The doubling cube
To speed up match play and to increase the intensity of play and the
need for strategy, a doubling cube is usually used. A doubling cube
is a 6 sided die that instead of the numbers 1, 2, 3, 4, 5, 6 on it,
has the numbers 2, 4, 8, 16, 32, 64 on it. If a player believes his
position to be superior he may, before rolling the dice on his turn,
double, i.e., demand that the game be played for twice the current
stakes. The doubling cube is placed with the 2 side face up to show
that the game's value has been doubled. His opponent must either
accept the challenge or resign the game on the spot. Thereafter the
right to redouble (double again) belongs exclusively to the player
who last accepted a double. If this occurs, the cube is placed with
the face of the next power of 2 showing.
The game rarely is redoubled beyond 4 times the original stake, but
there is no theoretical limit on the number of doubles. Even though
64 is the highest number on the doubling cube, the stakes may rise
to 128, 256, 512 and so on.
Beavers
A common rule allows beavers - the right for a player to immediately
redouble when offered the doubling cube, while retaining the cube
instead of giving it back up. (The redouble must be called before
the originally doubling player rolls the dice.) In this way, the
stakes of the game can rise dramatically.
Beavers are commonly allowed when backgammon is played for money
game by game, and usually not allowed in matches.
Jacoby Rule
The Jacoby Rule makes gammons and backgammons count for their
respective double and triple points only if there has been at least
one use of the doubling cube in the game. This encourages a player
with a large lead in a game to double, and thus likely end the game,
rather than see the game out to its conclusion in hopes of a gammon
or backgammon. The Jacoby Rule is widely used in money play, but is
not used in match play.
Crawford Rule
The Crawford Rule makes match play much more fair for the player in
the lead. If a player is one point away from winning a match, his
opponent has no reason not to double; after all, a win in the game
by the player in the lead would cause him to win the match
regardless of the doubled stakes, while a win by the opponent would
benefit twice as much if the stakes are double. Thus there is no
advantage towards winning the match to being one point shy of
winning, if one's opponent is two points shy!
To remedy this situation, the Crawford Rule requires that when a
player becomes one single point short of winning the match, neither
player may use the doubling cube for a single game, called the
Crawford Game. As soon as the Crawford Game is over, any further
games use the doubling cube normally.
Not quite as universal as the Jacoby Rule, the Crawford Rule is
widely used and generally assumed to be in effect for match play.
Automatic Doubles
When Automatic Doubles are used, any re-rolls that players must make
at the very start of a game (when each player rolls one die) have
the side-effect of causing a double. Thus, a 3-3 roll, followed by a
re-roll of 5-5, followed by a re-roll of 1-4 that begins the game in
earnest, will cause the game to be played from the start with
4-times normal stakes. The doubling cube stays in the middle, with
both players having access to it. The Jacoby Rule is still in
effect.
Automatic Doubles are common in money games (upon agreement). They
are never used in match play.
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