We can determine expected wins using pythagorean wins, which were first developed for baseball:
(runs for)2/[(runs for)2 + (runs against)2]= expected win %This can be applied to other sports as long as the coefficient is adjusted to better match the scoring of those sports. There is a very complicated formula that you can follow to find the coefficient, but for the major sports you can look this value up. For the NFL, the proper coefficient is 2.37.
We can use these expected wins to identify teams that are over- or under-performing.