I found a method a couple of years ago in a magazine feature about Russ Culver. He outlined the following formula for NFL games:
(QB rating of team's starter - QB rating allowed) + [(ypr - ypr allowed) x 10] divided by 4 = power rating
All of these figures can be obtained at the usatoday.com NFL team statistics page. "Ypr" is yards per rush average.
The resulting power rating needs some fine tuning, but it is a good place to start. After all, it helped Russ win the NFL Handicapping Championship in Vegas a couple of years ago.
Good Luck.
