ARM
Fan of chipmunk-like mascots.
I'd say that the most fair decision in that case would be that both UW and BSU would be given a percentage for that series that is the average of their other series percentages. So if UW goes 1.000 versus UM, MSU, and SCSU, .750 against UMD, and .625 against OSU, then they would get an a percentage of .875 for the unplayed BSU series. Meanwhile, if BSU didn't play OSU in addition to UW, was .500 against UM, SCUS, and MSU, and .250 against UMD, the Beavers percentage against UW and OSU would both be .4375. Or you could look at this as simply taking the average of the series percentages. It's not fair if you don't get to play a weaker opponent, but there are already other things that aren't fair, like a disparity in home and away games. However, I think it is worth trying to make the math as unbiased as possible.What if all the opponents aren't 'common'?
What do you do if, for example, Wisconsin's one and only series against Bemidji gets wiped out by COVID? Give Wisconsin a 1.0 because they probably would have won? Give them a zero because 'too bad, so sad'? Split the baby and give them 0.5?