Chris Borland - Wikipedia
49ers' Chris Borland, 24, retires because of brain injury concerns - Los Angeles Times
SF's Borland quits over safety issues - ABC7 San Francisco
Chris Borland, 24, says he's leaving the NFL because he fears a career of concussions. What do you think of his decision? By CNN
Chris Borland's Retirement an Uncommon Choice—but One NFL Players Understand, News, Scores, Highlights, Stats, and Rumors
NFL players react to Chris Borland's surprise retirement - Sports Illustrated
49ers Chris Borland retires from football, citing concern over head injuries - Field Gulls
Parents rethink youth football as safety fears drive NFL linebacker to retire at 24, NFL
Chris Borland's NFL Retirement Cost Him Millions, But Could Add 2 Decades To His Life, Statistics Show
NFL: Early retirements over health fears may have ripple effect
NFL doctor: CTE 'rare,' football safe - ABC7 New York
49ers LB Chris Borland won't be last to retire early for safety reasons - Sports Illustrated