I'm going to disagree here. Star players have too much to lose eg: endorsements, reputation, HOF, hundred million dollar contracts, etc.
Football would be exceedingly difficult to rig as would baseball*. If I wanted to rig a sport, it would be basketball and I'd find a way to gain leverage over one of the guys on the bench, like the sixth through eighth guy. If he misses a couple shots, plays some sloppy D, no one is going to think twice except maybe his teammates and coach, and they might just think he sucks. He's not rolling in dough the way the stars are and doesn't have the endorsements either.
- Unless you're a pitcher or QB, you're ability to influence a game is greatly diminished. And what could you possible offer a pitcher or QB to throw a game? These guys are already making beaucoup bucks. Only in basketball (or Hockey or Soccer) do you have players who play both offense and defense and who touch the ball enough to make a difference in the final outcome.
Personally, I think the position that would be most susceptible to rigging a game in the NFL (specifically, point shaving) would be the place kicker. No other single player has as much control over putting points on the board. If you pull a 41 yard field goal right, who's to say you're just not having a bad day. And you're team lost by 6 so it's not like the loss is on your shoulders (but your team was getting 3.5......)