Title Change


You may have noticed I have changed the title of this blog, I have also changed the “What is this Blog About” page.  I am still struggling with finding time to write much here, and I have certainly lost the original theme of the blog. Hopefully what I do post will still be of benefit, but all I can say right now is the blog is “about Backgammon.”


Opening 21

Yes, I know, I am not being consistent at all with what I am posting here based on the stated theme, but part of me is still trying to get a handle on the best way to learn this game, so I am going all over the place. For those few readers I have hopefully you will understand and bear with me, otherwise by blog becomes simply a place for me to try to organize my own study which is okay as well.

Opening Roll Source Material

Most of the information I am using for my study of opening rolls is coming from the opening information at http://www.bgonline.org/., these are often referred to as “Stick’s” rollouts because bgonline is maintained by Stick Rice. Timothy Chow, who comments here frequently, has published a very handy summary of 2nd roll information which can be found at http://www-math.mit.edu/~tchow/2ndmove.shtml. You will also find on Timothy’s page links to information on nactation, a link to a similar summary of opening moves using standard notation, and a link to the opening information on Tom Keith’s Backgammon Galore site. I will not bother to duplicate those links here at the moment.

These charts are very handy, but I am finding that to get a grasp on the material I need more than that, so I am attempting to group and offer some reasoning for the plays in an attempt to more easily learn what to do rather than rely on brute force memorization. I am also trying to get more comfortable with using nactation, so I am using it mixed with traditional notation and simple descriptive text (eg, make the 20pt) below.

Opening 21

There are basically two options for playing the opening 21, slotting (21$, 13/11 6/5) and splitting (21S, 13/11 24/23).

My tendency has been to play 21S except at gammon-go scores where I tended to the slot. The rollouts indicate that 21$ is a slightly better play than 21S. One thing I did find surprising is that according to Stick’s rollouts 21$ is best even at gammon save scores, Keith’s rollouts differ from this but those are cubeless rollouts. However the difference in slot and split at GS in Stick’s rollout is very small, probably not statistically significant.

I have started playing 21$ instead of 21S as my typical 21 opening. I am still struggling with this in a couple of respects, one is mentally dealing with getting hit, especially after a roll of 64 where you end up with two checkers on the bar. More difficult for me at this point is playing my second roll when I am unable to cover the slotted checker. This is an area I need to work on.

Replies to 21$

Hit the slotted checker if possible except with 11.  This is pretty easy to remember as it seems quite logical. The only question that remains is what do with the rest of the roll, of course with 31 you don’t have a rest of the roll after hitting.

11: Is the one exception to the hit the slot if you can rule. The best play with 11 is to make your 5 and 7 points. (nactation: N). Hitting here is around a 0.03 error. Without doing a lot of work to try and understand this one it seems that the value of making the 3 prime and having a good shot at a quick 4 prime must outweigh the value of hitting. Still this seems like a less than obvious best play to me.

22: This one can gives me pause OTB as it is very tempting to make the 20pt – given all we hear about the value of doing that, but the best option here (based on Keith’s data and bot evaluations) is to hit the slot and make the 4 point. (nactation: e)

41: Play 24/23 with the second checker, the two other options of slotting the 5 or 7 pts leave too many return shots. (nactation: U)

42: Play the second checker down to the 11 pt, it gives you a builder and can only be hit with 65. (nactation: S)

43: Stick’s rollouts (which for 2nd rolls do not have any at score information) gives a very slight edge to playing 24/21 with the second checker, Keith’s are the same except at GG Keith’s play is down (13/10). This makes sense as you need to contain checkers for the gammon and getting the extra builder down improves you chances of doing this. (U, except at GG S)

44: Pretty easy, make the 20 pt and the 9pt. (B)

54: A very slight edge goes to bringing a checker down to the 8pt (S), running the checker out after the hit ( R) is not far behind although I find it surprising that R is not better at least at GS scores)

64: Easy, run your checker to the 14pt hitting both blots in the process. (K)

Split Against The Slot.  At first blush splitting when you cannot hit the slotted checker may not seem the best thing to do since you are giving your opponent two blots to shoot out and the slot gives them more ways to hit. However, some of the hitting plays that present themselves after these splits are not necessarily all that good for your opponent as they either bury checkers, force them off their 5pt, and/or leave good return shots.

32, 51, 52: S

21: Timothy’s chart gives both S and $ as options here, recent extensive 4ply XG rollouts by Neil Kazaross posted on the BGonline forum make it pretty clear that the $ is best, but the difference is still only 0.005 http://www.bgonline.org/forums/webbbs_config.pl?noframes;read=59007

62: Has 3 viable options S (24/18 13/11), Z (13/7 24/22) and N (13/7, 6/4). Running out with a back checker (R) and bringing two down from the midpoint (D) have also gotten consideration. Based on recent rollout data S is best with Z being close and N not totally out of the question. http://www.bgonline.org/forums/webbbs_config.pl?noframes;read=58683

63: Running a checker out (R) is the best play here rather than splitting, and the reverse split (24/22 13/7, Z) is slightly better than the normal split. None of the plays are huge errors (S being about –0.015 worse than R)

Rather Obvious Plays. 53, 55 both make your 3 pt, 65 always runs a checker on the 2nd roll except for against 61P where you can’t, and 66 is forced 61 make your bar point.

And Finally.  33: Make your 5 pt and the 22pt. This play is harder to remember than it seems because in many cases the 2nd 33 is not used to make the 5 pt even though that might seem like the logical play at first glance. My instinct with this play is to make my 5 and 3 pt because having two home board points seems like such a good idea. But that is behind the best play and the more typical 33 second roll play of making the 22 and the 10 (B).

Replies to 21S

Play Like First Roll.  Many of the replies to 21S are played liked the first roll—or at least like of the main options for the first roll. These are:

31P, 51S, 61P, 32S, 42P, 52S, 54S, 62S, 63S (or 63R), 65R

Other Non-doubles

21: Playing 24/21 (21U) has a very slight edge over 21S, but both are viable plays.

41K: Hit both blots in your home board.


53P or 53S: 53P gets an extremely small edge, but splitting is very close which is why I put it here rather than in the play like first roll group.

64H: Hit the checker on the 15 with 24/15


11e (6/5(2),24/22) – Against the slot 11 is played as N, but with the split playing N gives shots with 6s and 7s, so this requires a safer play

22N, make the 4 and 11 points.

33B, make the 21 and 10 points.

44B, make the 20 and 9 points.

33 and 44 are both difficult for me to keep in mind because I have to fight the desire to make the 5 point with them. Of course with 44 this is moving two from the 13, with 33 you still have 2 3s to play. While making the 5pt with a 33 on the second roll is right at times, making it with a 2nd roll 44 is almost never right. 

55A, Hit on the 1 and make the 3, giving you a good start on a blitz.

66B Same thing for 66 on all 2nd rolls except after 61P, where you can’t, B with a 66 makes both bar points.