I never really embraced the issue of CTE until I listened to a broadcast on a study of CTE.  Specific CTE study focused on trauma to the brain at an early age (prior to 12 years old).   Study indicated a higher CTE as adults those who had pre-concussive incidents  during the developmental period of the child's brain (9 - 12 years of age) versus those who were not.  Pre-concussive is not to be confused with a full on concussion.  "CTE has been linked with repeated concussions and involves brain damage particularly in the frontal region that controls many functions including judgment, emotion, impulse control, social behavior and memory. " ... also depression.   Do you stop your child from activities that promote pre-concussions?  The response was that decision is left those responsible for the well being of child.  Food for thought.