In The Rookie, field conditions (turf) affect play but I don't recall hearing anything about gravity or air density. Normally, I would give it any thought but in Sigler's case, he goes out of his way to think through a lot of the science.
Obviously, very small differences in gravity or air density would affect the game dramatically. Perhaps the environment is controlled locally in football stadiums as it would be on a space ship. In this case, I would assume it would be normalized to match Earth since that's where football was born.
Quyth tatoo artist
My blog: http://whatchuck.wordpress.com/
My music: http://www.myspace.com/chuckbrodeur