"Playing tackle football under the age of 12 exposes children to repetitive head impacts that may double their risk of developing behavioral problems and triple their chances of suffering depression later in life, according to a study published Tuesday in Nature magazine’s journal, Translational Psychiatry.

"The research, conducted by Boston University’s Chronic Traumatic Encephalopathy Center, provides the most powerful evidence to date that playing contact football before age 12 may cause brain changes throughout life."

http://www.bostonglobe.com/sports/2017/09/19/study-links-youth-football-greater-risk-later-health-problems/UF3vWIAraotnJnbU8o8TDP/story.html