Playing for Gammon

In saving the gammon we looked at how to avoid losing a gammon. Here is the other side: recognizing when you can and should push for a gammon win, and the basic techniques for getting it. A gammon counts double, so in a match it can move you much closer to victory in a single game.

The golden rule

Playing for a gammon is only reasonable when you are a clear favorite, and even then it carries a risk: if things go wrong you can lose a game you could have won outright by doubling. That leads to the main rule:

If you play on for a gammon instead of doubling your opponent out, your chances of winning a gammon must be at least twice as large as your chances of losing the game.

Here is why. Suppose you are so strong that a double would be an easy pass. If you double, you collect one unit for sure. If you play on instead:

• a single win still gives you one unit, the same as cashing;
• a gammon gives you two units, one more than cashing;
• a loss costs you one unit, two less than cashing.

Each gammon gains one unit over cashing and each loss costs two. So you need two gammons for every loss just to break even. The same logic holds when the cube is already on 2 or higher; only the size of the stakes changes.

Two caveats. Under the Jacoby rule, often used in money games, gammons do not count unless the cube has been turned, so with a centered cube there is no point in playing on for one: double and collect. In match play the score can change the value of a gammon a great deal, for example after the Crawford game.

Estimating your gammon chances

The decision rests on two numbers: your gammon chances and your losing chances. Judging them accurately without a computer takes experience. Some guidance:

• The more of your opponent's checkers are trapped, on the bar or stuck deep in your home board, the higher your gammon chances.
• Several opposing checkers piled on your ace point are a typical sign of a strong gammon position: they are out of play and he will need many rolls to bring them home.
• Your losing chances depend mostly on whether he still has a realistic way to hit a shot.

Analysis tools such as GNU Backgammon and eXtreme Gammon show gammon and losing chances separately. Checking a few of your own positions with them is the quickest way to develop a feel for these numbers.

It is not a one-way road

Deciding to play for a gammon does not mean you must play to the bitter end. You are still the favorite, so if things start going wrong you can usually double within the next turn or two and secure the game. Do not wait too long, though: if your position slips far enough, your double turns into a take, and you are suddenly playing for higher stakes in a worse position.

Creating gammon chances

Many players miss chances to turn a good position into a real gammon position. The plays that do it are often bolder than the ones you would choose by instinct. Taking calculated risks is part of backgammon, and bigger rewards come with bigger risks.

Do not always play safe

Imagine you are a clear favorite and your opponent has one checker on the bar and a blot in your home board. You can play a quiet move that clears a point and leaves no blots, or you can hit the blot as well, putting a second checker on the bar while leaving a blot of your own. The double hit often wins far more gammons. Your opponent has to enter with two checkers against your board, and if he fails to hit back you can make new points or hit again next turn.

Full primes

One of the clearest gammon situations is a full prime with one or more opposing checkers trapped behind it. Even here the safest play is not always the strongest. If you can keep your prime intact and arrange things so that your opponent's forced entering move leaves him exposed, you may be able to pick up a second checker. Two checkers trapped behind a full prime raise the gammon chances a lot. Read more in six-point primes.

Conclusion

When you lead and want a gammon, you often need to choose a bolder play than the safest one, because the reward justifies the risk. Stay alert all the same: when you go for the gammon there is always a chance of losing, and that loss costs more than the gammon gains. Remember the rule: two gammons for every loss. And as soon as the position stops looking that good, double while you are still the favorite. For the cube basics, see the doubling cube.