[kretara]

If you want a sport that really requires an athlete then how about Rugby?

Another thing to consider. How many personel substitutions the "team" has per game. American Football is unlimited which means that individuals (for the most part) only have to be in for a few downs and each down is something like 10-25 seconds of movement.
Soccer has a limit of 3 substitutions per team.

I don't follow hockey, baseball or basketball so I'm not sure about them.