After killing four and taking his own life, Shane Tamura — a former football player at two L.A.-area high schools — left behind a suicide note, authorities say, alleging he had the brain disease CTE.

A 2017 study found that more than 87% of football players tested across all levels — high school, college, and pros — tested positive for Chronic Traumatic Encephalopathy.

Young athletes (ages 6–14) in tackle football experience vastly more head impacts — up to 15 times more — and 23 times more high-magnitude impacts compared to flag football participants [3]. Even subconcussive hits that do not cause symptoms can lead to cumulative brain injury and are not prevented by helmets alone [4].