There is something called the FIBS rating.
It's a weighted ratings system. A player with a low rating will see their rating rise higher if they beat a player with a high rating than they would if they won a match against a low rated player. There are other factors too. The main one being the match length. Winning a match played over a series of games, with the winner being the first to amass 21 points would yield a bigger ratings gain for the winner than a match against the same opponent that was played over 1 or 3 points.
Backgammon is more like poker than chess. It's not about pure skill. There is an element of luck too. A good player will beat a bad one most of the time, especially over a series of games. Yet perfect play will sometimes be confounded by mediocrity combined with luck. It's all about probabilities, and making the optimal play, so that you maximise your own chances of a useful throw of the dice, while doing your best to minimise your opponents options.
Meanwhile, of course, your opponent is trying to do the same thing to you.
Once you reach a certain level, and can play the best possible move every time (which no human ever does, although computers increasingly can) if you meet an opponent that is equally skilled, it becomes a matter of luck.
The human factor dictates style. For example, if an attacking option and a defensive option both present themselves, each offering some balancing factors of risk and/or reward, one player might choose the aggressive play, while another might make more conservative choices. Each may prevail. That's the game.
Watching England play against Tunisia last night, I couldn't help feel that against a better team, (and if it had been chess, rather than backgammon, England would prabably have won 4 or 5 - 1 )given the same luck, they would have struggled.
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