Score-based cube actions

Mastering the doubling cube is hard to do; however, in certain conditions, the decision can be automatic. Below are some cubing scenarios that arise often during matches that tend to surprise newbies, but make perfect sense when you think about it and should be committed to memory.

Post-Crawford automatic doubles (1a cubes)

As we’ve mentioned in a previous lesson, most backgammon matches implement the Crawford rule, where you set the cube aside for a single game once the first player reaches a score of 1a. After this game, the trailer should automatically offer the cube at their first convenience. They have nothing to lose and everything to gain by doing so — their opponent cannot recube and will win the match if they win their next game anyway, so might as well play for 2 points instead of 1.

Free drop

The free drop is the leader’s analog to the automatic double as a consequence of every post-Crawford game being worth 2 points. It’s easier to explain by example: consider a match scored at 6a-1a. With the cube being turned immediately every game, that means instead of needing to win 6 single games, the trailer needs to win only 3. If the score was 5a-1a instead, the trailer would still be looking to win 3 games to win the match. Trailing only 5a instead of 6a turns out not to provide any advantage whatsoever.

We therefore conclude that when the trailer is an even score away in post-Crawford (for example, 6a-1a), the leader has the option to drop a cube for free. They should do so whenever they have any negative equity, even with only 49% win chances. This results in some strange-looking sequences where the trailer will start with a great roll (maybe rolling 31: 8/5 6/5, making the 5-pt), double at their first opportunity, and the leader will drop after 2 rolls.

Automatic redouble

Another “have nothing to lose” doubling action by the trailer occurs when the score-leader offers the cube at a score that could win them the match. For example, suppose the score is 2a-4a, and the leader offers the cube. If taken, the game will now be played for 2 points, which is enough for the leader to win the match. The trailer might as well redouble the cube and play for 4 points instead. The trailer has nothing to lose and everything to gain.

Automatic redoubles should be considered when leading and considering doubling, as well. When you are leading and only 2a, you should know that if you offer the cube, your opponent will surely be sending it back, and the game will be played for 4× the points and not just 2×.

2a-2a

The last scenario, which is the most subtle, is what to do when the score is 2a-2a. Basically, just D/T immediately. The idea is that at this score, once the cube is turned it’s the final game of the match. Therefore, as soon as one player has an advantage (even a 51% win chance) they should double. There is no chance of being recubed or doubled out anymore, and so there is no need to fear and hold off for a stronger position to double.

Further reading:

• An article by Kit Woolsey on the automatic double at a score of 2a-2a.