the dorbel daily

Wednesday, 28 September 2011

Just Whack It.

We all go there, the game's nearly won, we are rolling a prime home, but the opponent pops up a blot. What to do, hit it or ignore it? Inevitably the opponent has a strong home board. If she doesn't, it isn't a problem because we don't risk much with the hit. What's the rule? As ever, it depends. Look at Position One.
Black leads 2-away, 3-away, the cube is in the middle and White has a checker on the bar. Black is correctly playing on for a match winning gammon. What to do here, hit or make a quiet play?

One way to approach this problem is to estimate your gammon chances if you hit and your gammon chances if you play safe and adjust those for the gammon price at this score and ideally do the same for your opponent, bearing in mind that at this score her gammons will be almost as dangerous as yours, getting her to Crawford. You can also look at the weather forecast, your horoscope for the day and the stock exchange closing prices, but we are already doing too much work. Just whack it! Why? I use the Glad/Sad ratio. If we hit, White dances 70% of the time and we are very Glad. We are big favourites to closeout and win and with two checkers on the bar and three other crossovers that White needs on the far side, we win over 50% gammons. Closing out two checker is usually 40% or so and three crossovers is a roll and a half. When White hits (30%) we are a bit Sad, but we still have some chances to enter and jump and if we can do that we must pick up two more checkers! If we play quietly and White rolls a two, then we will probably turn the cube and cash, so no gammons there at all. A 70/30 Glad/Sad ratio is pretty hot at any time, hotter here when the 70 contains 50 gammons and the 30 just means we get doubled out.
Now you may criticise this technique as crude and point out that it ignores many other possibilities. You'd be right. I haven't counted the times after the hit when we fail to cover, or the times when we choose not to hit and still make the 2 point next turn anyway. I haven't allowed for the possibility that White may be able to double us in and win a doubled gammon. On the other hand the attempt to be more precise and estimate gammon rates also suffers from this problem.
There is another reason why we need to hit here. We do need to make the point for the bearoff and every roll that we wait to throw a natural point making number it gets harder. It's harder to make the deuce than it would be to make the ace, because there are fewer checkers to do it with. One enemy checker on the deuce, or even an empty point and men on the bar can be very inconvenient, a phenomenon known as a phantom deuce point game.
Convinced yet? OK, if you are White in that position, do you want to be hit or would you rather be left alone? If White would rather be left in peace, it must be right to hit it. Always do what the enemy doesn't want you to do. I must stress that in this position, the unusually high value of gammons to Black is key. If a gammon didn't count for much, no need to let White back into the game by giving her a shot. Let her have her deuce point game by all means. It doesn't ever win, because you will just double her out.

This next position illustrates some of these points. Black leads 2-1 to 5 and has the cube, White is on the bar.

In the first position, Black's Gammon Price is 1, twice as valuable as for money. Here on the other hand, it is .40, less than for money. The GP in a match is your ME for winning a gammon minus the ME for a plain win, divided by the ME for a plain win minus the ME for a plain loss.
Here that is 100-83/ 83-40 or .40. So, here, hitting here would be quite wrong, partly because we don't gain much from a gammon anyway, partly because it is easier to make the ace than the deuce and partly because we risk a horrendous gammon loss, with the whole match down the drain.
To use the Glad/Sad test it is split 70/30 like before, but now the Glads are fairly Glad, but the Sads are very Sad indeed, going behind in the match when we lose a plain game and losing the whole thing when we get gammoned.

By all means go for a pure analytical approach, where you need an accurate estimate and an accurate use of some mental arithmetic. If you can cope with that, then this is what most of the top pros do. For most of us though, me included, instinct and experience need to stand in for the hard slog of calculation. Just Whack It!

By the way, failing to hit in position 1 is a small error, hitting in position 2 is a blunder!

Until the next post, enjoy the game!

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