Until recently we (the medical community) thought that concussions were pretty innocuous. Sure the blow to the head might cause brief loss of consciousness or change in mental state (stunned, confused, etc) but it was believed that it caused no residual brain damage.
All that is changing: cumulatively concussion can and does lead to “chronic traumatic encephalopathy”. While it was first described in professional athletes who have taken repeated severe “shots” to the head, recent studies have found it in kids as young as 18 years old.
The long-term symptoms of this disease are mood changes, anger management problems, Alzheimer’s-like symptoms, and death.
Certainly more study is needed, but in the interim we need to be aware that this can start in teens. We need to take “simple” concussions very seriously, and maybe we shouldn’t expose the adolescent brain to forces and activities that can damage it.
Make good choices, don't take chances