49ers Chris Borland retires amid head trauma worries
Chris Borland, Fearing for Health, Retires From the 49ers. At 24. - The New York Times
Chris Borland retires from NFL aged 24
Another young NFL player calls it quits to protect future health
NFL Running Back Andre Williams On Chris Borland's Retirement
Chris Borland talks 'early' retirement in UW-Madison guest lecture
Traumatic Brain Injury Isn't Just an NFL Problem
Rookie NFL linebacker calls it quits
ABC7 SPORTS: 49ers player Chris Borland makes unprecedented retirement decision - ABC7 San Francisco
49ers Linebacker Quits After 1 Season, Citing Safety Concerns : The Two-Way : NPR
Chris Borland: Young American football player retires over concerns of brain injuries, The Independent
San Francisco 49ers linebacker Chris Borland retires over head injury concerns - ESPN
San Francisco 49ers' Chris Borland retiring from NFL
49ers' Chris Borland retires: NFL responds, cites safety progress - Los Angeles Times