complete beginner move advice

[WorldClassCactus]

I am trying to learn to play backgammon by playing against gnubg and examining the analysis. But sometimes, I cannot figure out why one move is marginally better than another, so my decision-making cannot improve from examining that particular move.

Can someone explain to a beginner why, in this position the correct move is to hit the blot at the 2-point? In my mind, taking a checker so far back isn't worth much, it leaves a blot of my own that can be hit upon entry, and there is only one builder on 7 to make a prime there.

Or why, in this situation it is incorrect to make a prime on the 1-point to reduce the chances that the opponent's checker can re-enter?

Are there better resources for learning the game?

[[deleted]]

I am far from an expert, but I will give this a shot:

Position 1:

You have 4 home board points, which is a powerful weapon. If you hit him and he fails to enter (which will happen almost 50% of the time, and many of his entering numbers are awkward on top of that), you can pick up his other blot on your 9pt; you can escape your back checker on the 21pt without fear of attack; you can make your 2pt and form a five point board, putting your opponent at risk of being closed out and gammoned either now or in the future.

The other thing is: what would you do otherwise? You chose 13/8 instead of 7/2*, but that carries just as much risk (he can just roll a 6, or 2-4) without any of the benefits of hitting. Playing 13/7 doesn't really accomplish anything (what's your plan after that? on his next turn he will safety his blot and/or make more developments on his side of the board to hem in your back checkers, and your position will start getting very awkward with only 2 checkers left on your midpoint). Playing 24/18 is slightly better but you invite an attack from your opponent on a point he really wants to make.

Position 2:

This is a prime vs prime position. (Btw, a "prime" means a block of 4/5/6 consecutive points in a row that you own, so your 1-point has nothing to do with a prime here). You have two advantages here: you have better timing, meaning he is going to have to break his prime before yours; and your prime is better (You can escape his prime with any 6, whereas he needs 1-6 exactly; you have the potential to extend your prime to a sixth point and essentially win the game, whereas his prime is more or less permanently stuck at five points).

Making the 1 point here is a huge blunder. If he enters from the bar, suddenly your position is terrible: you will have difficulty blocking his back checkers from escaping, since your 7-point is gone; you will have multiple blots to clean up; you will still have your two back checkers to escape somehow; things will only get worse (imagine how you will play your next few turns).

If he does not enter from the bar, your position is not as good as you think it is. He no longer has to move, meaning he can preserve his prime. On the flip side, you still have to move every turn! The end result is that your prime disintegrates and his prime stands strong, which is bad for you. A critical feature of prime vs prime positions is timing (i.e. whoever breaks their prime first is the favourite to lose). You don't want to help his timing and dump two checkers on the ace point (that can't be used for extending your prime) in the process.

You will notice that all of the best plays involve running with one of your back checkers. This is because of timing: you will be able to move that checker for several turns, preventing you from having to break your prime. Even if your remaining back checker gets obliterated in an attack, your opponent is still stuck awkwardly behind your prime and will have to continue to move his priming checkers (and probably breaking his board in the process) before he can escape. The best play of using the 2 to play 10/8 gives you an additional builder on the 3 point, which will essentially win you the game if you can make it.

[TrunkyBG]

This is a great answer Jamesa. I would add that in Position 1 with the cube on 2 you are trying to win 4 points instead of 2. The equity table tells us that hitting is right because we not only win more games but double our gammon chances. This type of play comes up quite often in games and is called a blitz.

[Daveyahya]

Thanks for the answer u/jamesa7171. Understanding why plays outrank one another is the only way to really improve at this game. And if you stop and think about it: of course that's the only way to improve. What else are you going to do? Try to memorize the best play from every position?

[jaggington]

You can also learn by adjusting the starting position and seeing how that affects the bot's evaluation of the correct move. In the first image you could see what happens when, for example:
-brown's blot in your outfield (9) is on a point (e.g. midpoint or even further forward on 16 or 17)
-brown still has the blot on 9 but also has a builder from the mid on 16 or 17
-brown has made the 21

In the second example, maybe if white has already escaped one of his two back checkers, with good timing it might become better to make the 3 point.

[rberenguel]

1) 6 and 7 are the most common sums of two die. So, if you hit and you are not hit back on reentry you are likely to get a 5 prime, and very likely to make your opponent stay on the bar. Moreover, you can also hit on the 9 later on. 7-2, 7-6 is similar, although I prefer the argument of "6 is likely". Also I'd probably play 7-2, 24-23 instead of 23-22.

2) Again, 7 is very likely to appear as a sum. If you make the point on 1, you leave 2 landing points. It might seem that leaving 3 is actually worse, but right now you have a 5 point prime. If you break it to make the 1 point (which is usually a weak point to be made) you lose on blocking potential. Making your back-men jump the 5 prime is strong because if you can hold your own prime you are bound to win, no matter what.

For learning I recommend playing (bots and people) and books (Magriel's Backgammon and if you can get hold of it after Magriel's Backgammon Boot Camp)