Chris Borland Retires at Age 24 Over Concussions
How former San Francisco 49ers Chris Borland's retirement could change NFL forever - ESPN
49ers linebacker Chris Borland retiring at 24 due to long-term health concerns
San Francisco 49ers Chris Borland retires over repeated head trauma
Andrew Luck joins Jim Brown, Barry Sanders among NFL's most stunning retirements
49ers LB Chris Borland won't be last to retire early for safety reasons - Sports Illustrated
49ers ex-linebacker Chris Borland salutes Pat Tillman
49ers' Chris Borland becomes latest young NFL star to retire early - Cincy Jungle
Chris Borland retires from 49ers after one year due to fears over head trauma, NFL
Chris Borland's NFL Retirement Cost Him Millions, But Could Add 2 Decades To His Life, Statistics Show
Retiring 49er Chris Borland to pay back NFL signing bonus - Sports Illustrated