Doubling in a tournament - Backgammon double
In a 9-point match with the score 8-7 in your favour you would not double your opponent. Whether you win 9-7 or 10-7 makes not the slightest difference to the result. Your double simply adds to the risk, for should your opponent win his score will jump to 9 making him the winner of the match.
Conversely, if you are in the losing position with the score 7-8, you must double at the first opportunity, right at the beginning of the game. If you lose this game you are out of the contest, so double your opponent at the start and then if you win you win the match. This starting double puts pressure on your opponent and increases the chances of his making an error.
If the score was 7-5 in favour of your opponent in a 9-point match, and he doubled you, and assuming that you considered it correct to accept the double, then on your next turn you would re-double him to 4. Again you have nothing to lose. If you do not win you have lost the match, so force him into either conceding the game and giving you 2 points, or to play for 4 points so that if you win you win the match. A re-double of this nature is very disconcerting for your opponent.
Because of this situation where the losing player can, by wild use of the doubling cube, sometimes snatch victory from a superior player (perhaps by use of a double combined with a lucky backgammon), the Crawford rule came into existence and is now frequently used in tournaments. This rule states that when one player is one point away from victory the doubling cube cannot be used for that one game. After that game the cube may again be used as before. This gives the player who has come close to victory a safe game in which his opponent cannot snatch victory with a wild double.
In an elimination match you treat the doubling cube with great care, and before you use it weigh up the consequences of an instant re-double. If you are leading in the match, be very cautious and double as little as possible. If you are losing the match use it freely. The winner has to play with the greater caution and must quite frequently refuse your double to give you a point, rather than risk a 2 point loss. Hesitate to double the winner when he needs only 2 points to win as a lost game in this situation costs you the match.
If you are up against a less skilled player refuse doubles that are based on lucky situations. For example, in a running game in which the two sides have no contact (i.e. the men have disengaged), where the fickle dice will decide the issue, you would refuse the double. If you had been playing for money the probabilities might well make acceptance of the double the right thing to do, but in this situation you do not cast away 2 vital points on the luck of the dice. You should prefer to accept doubles where superior skill can help you.
In end game play never accept doubles if your chances are much below 50%. When playing for money you accept these doubles, not because you expect to win but because by accepting you actually lose less money than by resigning. In a knockout tournament the law of large numbers does not apply. You can only lose once, so refuse doubles where probability is not on your side.