Chris Borland, San Francisco 49ers linebacker, retiring due to head trauma concerns - Newsday
Chris Borland retires from NFL aged 24
NFL Player Chris Borland Retires Due to Concussion Risk
How San Francisco 49ers' Chris Borland made his decision to retire over safety concerns - ESPN
San Francisco 49ers Chris Borland retires over repeated head trauma
Chris Borland's NFL Retirement Cost Him Millions, But Could Add 2 Decades To His Life, Statistics Show
Another young NFL player calls it quits to protect future health
49ers Linebacker Quits After 1 Season, Citing Safety Concerns : The Two-Way : NPR
49ers' Chris Borland Retires at 24 Due to Concerns Over Head Trauma and Safety - TV Guide
San Francisco 49ers linebacker Chris Borland retires due to health fears, NFL News
Chris Borland: Young American football player retires over concerns of brain injuries, The Independent
Two Stories, One Reason: Why An Actor And An Athlete Refuse To Support Football
Chris Borland Retires: NFL Says Football 'Has Never Been Safer'