Rules of the Game ================= This section describes how to play a game, a match, or a session of money games against **GNU Backgammon** or a human opponent. It is adapted from the rules section of `Backgammon Galore `_, courtesy of Tom Keith. Setup ----- Backgammon is a game for two players, played on a board consisting of twenty-four narrow triangles called *points*. The triangles alternate in color and are grouped into four quadrants of six triangles each. These quadrants are referred to as a player's *home board* and *outer board*, and the opponent's home and outer boards. The home and outer boards are separated by a ridge called the *bar*. .. figure:: images/rulfig1.png :alt: A board with the checkers in their initial position **Figure 1.** A board with the checkers in their initial position. The points are numbered for each player starting from their home board. Each player has fifteen checkers. The starting position is: 2 checkers on the 24-point, 5 on the 13-point, 3 on the 8-point, and 5 on the 6-point. Each player has their own pair of dice and a dice cup. A doubling cube (values: 2, 4, 8, 16, 32, 64) is used to track stakes. Object of the Game ------------------ The goal is to move all checkers into your home board and bear them off before your opponent. .. figure:: images/rulfig2.png :alt: Direction of movement of White's checkers. Red's checkers move in the opposite direction. **Figure 2.** Direction of movement of White's checkers. Red's checkers move in the opposite direction. Movement of the Checkers ------------------------ To start, each player rolls a die. The higher roll goes first, using both dice values. Turns then alternate using two dice. The roll indicates how many points a checker may move (forward only). Rules: 1. Checkers may move to *open points* (not occupied by two or more opposing checkers). 2. Dice values are separate moves. For example, a 5 and 3 roll can be two moves or one combined move if the intermediate point is open. .. figure:: images/rulfig3.png :alt: White opens the game with 5-3. **Figure 3.** White opens the game with 5-3. 3. Doubles are played twice (e.g. 6-6 gives four 6-point moves). 4. A player must use both numbers if legally possible. If only one number is legal, the larger must be played. Hitting and Entering -------------------- A single opposing checker (a *blot*) can be hit and sent to the *bar*. Barred checkers must re-enter before other moves. Re-entry is done by placing the checker on a point in the opponent's home board corresponding to a rolled number, if that point is open. .. figure:: images/rulfig4.png :alt: White rolls 6-4 with a checker on the bar. **Figure 4.** White rolls 6-4 with a checker on the bar. If neither point is open, the player forfeits the turn. All checkers must be entered before continuing with other moves. Bearing Off ----------- When all checkers are in the home board, a player may *bear off* by rolling a die corresponding to the checker’s position. If no checker is on that point, use a higher-numbered one. If none are available, the turn is forfeited unless another move is legal. .. figure:: images/rulfig5.png :alt: White rolls 6-4 and bears off two checkers. **Figure 5.** White rolls 6-4 and bears off two checkers. A player must re-enter any hit checkers before continuing to bear off. Doubling -------- Backgammon can be played for stakes. Each game begins with a value of 1. A player may propose doubling at the start of their turn. - The opponent may accept or concede. - The doubling cube passes to the acceptor, who alone may re-double. - There is no limit to redoubles. Gammons and Backgammons ----------------------- At game end: - If the loser has borne off at least one checker: they lose 1x the cube value. - If not: they are *gammoned* and lose 2x. - If not and they have checkers on the bar or opponent's home board: they are *backgammoned* and lose 3x. Optional Rules -------------- 1. **Automatic Doubles**: If doubles are rolled on the first turn, cube goes to 2. Usually limited to one per game. 2. **Beavers**: When doubled, a player may immediately redouble while retaining the cube. 3. **Jacoby Rule**: Gammons and backgammons count only as singles if no double was offered during the game. Match Play ---------- Matches are played to a point goal (e.g., first to 5). The Crawford rule prevents doubling in the first game after one player is within one point of winning the match. +------------------+--------+--------+-----------------+ | Match to 5 | White | Black | Doubling | +------------------+--------+--------+-----------------+ | White wins 2 | 2 | 0 | Allowed | | Black wins 1 | 2 | 1 | Allowed | | White wins 2 | 4 | 1 | Allowed | | Black wins 1 | 4 | 2 | *Crawford Game* | | Black wins 2 | 4 | 4 | Allowed | | White wins 2 | 6 | 4 | Allowed | +------------------+--------+--------+-----------------+ There is no reward for winning by more than the required number of points. Note: Automatic doubles, beavers, and the Jacoby rule are *not* used in match play.