I played with some monstors at Kahuku.  All my years there, I only had one teammate get a concussion.  We hit/tackled hard too  of course we hit just as hard playing tackle football at Laie park, BYU-H fields, the grass at the old chapel, or at the beach so it was no change when we got to HS.

My main point was that the coaching in 7th and 8th was so bad that my kid got two concussions before even getting to HS (as well as a broken clavical).  And they happened in drills that were absolutely stupid or run in such a bad way that it was bound to happen.  

So I don't trust any of the coaches from 8th grade down.  They are absolutely aweful.  I was so mad I wanted to give the coaches an old fashioned Samoan sasa.  And before anyone starts saying sasa is a dance, we used to call a "whipping" a "sasa" too.