Say the average shooting percentage in a league was 50% and we decided to rate all teams against the hypothetical opponent X, who shoots 50% on offense and allows 50% on defense.

Now let's say that we've calculated the following:

* On offense, Team A shoots 52.1% vs. the average opponent X.

* On defense, Team B allows the average opponent X to shoot 54.2%.

How would Team A be projected to shoot on offense w/ Team B on defense?

One could go this route and come up with a value: .50 + (.521 - .50) + (.542 - .50) = .563 = 56.3%

That would be a reasonable estimate. However, now let's try this example w/ the average shooting percentage still at 50%:

* On offense, Team A (a great offense) shoots 74% vs. the average opponent X.

* On defense, Team B (a very poor defense) allows the average opponent X to shoot 76%.

If we use the same equation, you get the following percentage for Team A on offense: .50 + (.74 - .50) + (.76 - .50) = 1.00 = 100%

I find that to be unlikely and, therefore, the method to be unreliable. Is there a statistical method to accurately forecast the offensive shooting percentage of Team A in these situations?