To be fair, I believe that football players have, generally speaking, the same average intelligence as we see represented in our society. They are not expected to use it, since they have a different advantage, and find themselves at a disadvantage if they can't make it as a professional athlete. The sad reality is that they are treated differently by mainstream society from a young age, and this ends up hurting far more than it helps.
We celebrate the wrong things, and children want to be popular. Heck - kids will choose not to take "nerdy" classes because of the stigma associated with those classes.
I have a novel idea - what if we were to stop advancing kids who cannot manage to pass their classes? How about if we stopped allowing them to play any sport if they cannot manage to get a c average in all of their classes?
But, even without this knowledge, they have the intelligence. At some point they have to decide how they are going to use it.