As I mentioned in another comment, everything I said was speculation based on playing in high school and college. I don't have any strong evidence to back up my claims. That said, I'm skeptical of the numbers in the article you linked. I could be wrong, but in my experience players in high school were much more likely to report injuries than in college. Especially head injuries. Friends of mine in college, on multiple occasions, had headaches that lasted more than a week and refused to report them for fear of being benched or missing playing time. High school was the opposite, players would go to the trainers all the time for every little thing.

I can't argue with numbers, but I am just not convinced the method of data collection is accurate.