Backgammon and its variations make a little different game type from the "normal" board games on BrainKing.com. There is no square board with square fields, the game is played on a special triangles-in-two-rows desk. The other difference is that all moves are based on rolls of two dice which are randomly generated for each move. There are two sectors of the board called white and black home. White home is defined by 19-24 triangles and black home is made of 1-6 triangles. Each player starts with 15 pieces placed at specific positions:
The object is to remove all player's own pieces out of the board and avoid the opponent to do the same first. The game ends when all pieces of one player are removed.
Movement of pieces
When it is a player's turn, he/she must roll the dice and then move one or more his/her pieces according to the dice value. The dice are rolled automatically when the player on turn opens the corresponding game page for the first time (for this move). If the player tries to reload the game page or open it again later before making a move, the rolled dice will not change. The dice for the current move are displayed at the right half of the board (bigger dice) and the dice of the previous move of the opponent are shown at the left half of the board (smaller dice). If two different numbers are rolled, the player can make two moves at this turn. He/she takes the first (left-most) die value and moves one piece the same number of spaces. Then he/she does the same for the second die. Both moves can be done with the same piece or different pieces can be chosen for both moves. When two same numbers are rolled, the player can make four moves at this turn, all with the same die value (for example, if the dice show 5-5, four 5-spaces moves can be done). The white player moves the white pieces anti-clockwise (from the "1" triangle to "24") and the black player moves the black pieces clockwise. These pictures display one white and one black move (before and after the move):
The pictures above show that white moves one piece six spaces (from 9 to 15) and one piece three spaces (from 1 to 4).
The pictures above show that black moves four pieces four spaces (from 24 to 20, from 13 to 9, from 13 to 9 and from 6 to 2).
How to capture opponent's pieces
The player captures an opponent's piece when he/she moves a piece to the triangle occupied by only one opponent's piece (it is called blot). After such move, the captured piece is removed from the board and placed to the bar. The following picture shows an example of white capturing black pieces (from 17 to 20, before and after white move).
How to remove own pieces out of the board
The player can remove his/her own pieces when the following conditions are fulfilled:
All player's pieces are at the player's home. It means that white has all his/her pieces on one or more triangles of the 19-24 range and black's pieces must occupy 1-6 triangles. The following picture shows the situation when this condition is fulfilled for white but not for black:
No player's pieces are at his/her bar.
The place to move the piece according to the current die value would lie just after the last triangle. The picture above shows that white can remove a piece on 20 triangle because 5 is rolled.
There is one exception of the previous condition - if the removing move is longer than just after the last triangle but no other player's pieces stay at previous positions, such piece can be removed too. This picture shows that white has removed the piece on 20 triangle although his die shows 6.
Other important rules
The player cannot move a piece to the triangle occupied by two or more opponent's pieces (it is called block).
When one or more player's pieces are at his/her bar, the player must remove them from the bar before he/she can make a move with any other pieces on the board. The pieces of the bar are placed on the triangle of the opponent's home according to the current dice roll. All previous rules (same or different dice values, blocks, blots) are applied here too.
If the player cannot make a legal move, he is notified about this situation by a message "You cannot make a move" and must pass this move to his/her opponent by performing an "empty" move - clicks on one of sending buttons. Such move is displayed as "pass" in the game notation.
If a player wants to use the second die first, he/she must click on "Swap dice" link below the game board. There are several situations when the link is not shown:
Both dice show the same value.
The player could not make a legal move with the second die.
If it is possible, both dice must be used. It means that some pieces can become "frozen" in certain positions because making a move with these pieces would create a situation where the second dice couldn't be used.
If only one die can be used, the one with the higher number must be chosen.
A doubling cube
Backgammon (and its variants) is the only game which can be defined as a match that employs a doubling cube. The match is specified by the number of points a player must reach to win. The number of received points for a single game (which is a part of the whole match) depends on scoring rules and the doubling cube value - all details will be described in the next sections.
The cube is displayed at the right edge of the game board and its initial value is set to 1:
When a doubling cube is used in the game, each player begins a move with a choice to roll the dice (and make a normal move) or to offer a double. If a double offer is sent, the opponent must decide whether to accept it (and multiply the current doubling cube value by 2) or to reject it, which causes a loss of the current game and adding the doubling cube value number of points to the winner's score. Gammons and backgammons are not relevant when a cube offer is declined. (see Scoring in the next sections)
If a double offer is accepted, the player who accepted the offer becomes the possessor of the cube which is shown on the player's side of the board with the new value. The next picture displays the board after the first double accept:
The value of the doubling cube can be increased to 4, 8, 16, 32 and 64. After the first double offer is accepted, the next offer can be sent only by the cube possessor - it means the following double offers always alternate between the players.
After one player bears off all his/her pieces, the current game of the match is finished and the winner receives a number of points which depends on the final game position:
Single game (1 point) - the winner's opponent has borne off at least one piece.
Gammon (2 points) - the opponent hasn't borne off any pieces.
Backgammon (3 points) - the opponent hasn't borne off any pieces and still has some pieces either on the bar or in the winner's home area (the six pipes where the winner bears off own pieces).
This number is multiplied by the current value of the doubling cube - for example, if the cube shows 4 and the winner scores the backgammon (3 points), he receives 12 points to the match score.
Other important doubling cube rules
The match can be defined as a 3, 5, 7, 9, 11, 13, 15, 17, 19 or 21 points match.
If the winner's opponent has borne off at least one piece, the result is always the single game (1 point), no matter if some pieces still remain on the bar.
A double offer is not an option at the first turn of the game. The player who won the initial dice roll makes a normal move, then the opponent would have the first option of offering a double.
If a player is 1 point away from winning the match, he won't be given an option to offer a double because the reject would always won the match for him.
When a doubling cube value reaches the point where it would win the match for the player, the system won't show more options to double the cube value because it wouldn't make sense to increase it anymore.
Crawford rule: If a player reaches a score which is only 1 point away from winning the match, the next game is played as a Crawford round. In a Crawford round, the double cube is not used. If this round is finished and the match is not completed, the doubling cube can be used in all following games of the match.