berniesipe said:
Jim Brown would be an average back if he played nowadays 
I created a twenty four minute highlight film of Jim Brown which I uploaded to YouTube in three parts. Start here:
and follow to part two and part three. If you think any other back in history has has a combination of size, speed, balance, strength, intelligence, pass catching and throwing ability, I wish you would point him out to me. Notice that when you see highlight films of all the other hall of fame type backs, each usually has one or two types of runs that they excel at. Now think of Brown's runs: he overpowers when he has to, runs over guys if he has to, pirouettes, runs around people, outdistances almost everyone, manages to keep his feet when everyone else but Barry Sanders would be on his ass, come on...
I have seen all the great backs and the closest I have ever seen was Walter Payton and even he was a distant second. If backs without all Brown's talent have gotten 1500 to 2000 yards in a season since he retired, what makes you think that if he were in his prime he couldn't do it under these relatively easy playing conditions? A lot of smaller and slower backs have led the league rushing since he was around.