In football, a player can let the team down. A single player can make his peers better than they would have been without him. That's a huge incentive that we take away from the classroom with our constant emphasis on individual outcomes. In football, repetition is honorable. In the curriculum, we continually move forward, with not much opportunity to do things a second time and get better.
Students have to do new things every time they get to class.
In football, students do the same drills over and over all season long, and in fact get better at them. The skills get easier, and players start to use those skills to do things that are more complex. In football, the unexpected happens all the time. Every player will line up across from the same opposing player dozens of times during a game, but he knows that each time, his opponent could do something different and he'll have to react to it right in the moment. There's no opportunity to coast, to glaze out, to sit back and watch others work.