This is head-injury time for school athletes. With football, soccer, hockey and basketball, more players than not are likely to fall or be hit on the head, and many will be hit hard enough to get concussions.
Q 1: I think "players" are omitted between "than" and "not are..."
Q2 : I believe "many" is same people of "more players". Why was a same thing twice?
What do you think?
All the best,