Complex sentence: Many concussions that occur during high school football often go untreated and not monitored which is a big concern because repeated trauma to the head especially with concussion like symptoms puts a young athlete health at serious risk.
Split into simpler sentences: Many concussions that occur during high school football often go untreated and are not monitored. This is a big concern because repeated trauma to the head, especially injuries with concussion like symptoms, puts a young athlete health at serious risk.