Twenty-Four-Year-Old 49ers Linebacker Retires, Citing Fears of Brain Injury, East Bay Express
Ex-49ers LB Chris Borland doesn't think football can be saved
Chris Borland retires from NFL
Chris Borland Retires: NFL Says Football 'Has Never Been Safer'
Concussion Concern: LB Retires After One NFL Season
Chris Borland, San Francisco 49ers linebacker, retiring due to head trauma concerns - Newsday
How former San Francisco 49ers Chris Borland's retirement could change NFL forever - ESPN
24-year-old NFL player quits over concussion worries
San Francisco 49ers' Chris Borland retiring from NFL