Another young NFL player calls it quits to protect future health
NFL: Chris Borland retiring at 24, wary of head trauma
Linebacker Chris Borland says he'll repay part of signing bonus to 49ers - MarketWatch
Concussion Concern: LB Retires After One NFL Season
Chris Borland - Wikipedia
San Francisco 49ers Chris Borland retires over repeated head trauma
Borges: NFL takes big hit with Chris Borland”s retirement – Boston Herald
49ers' Chris Borland retiring at 24, wary of head trauma, Nation & World
Chris Borland retires from 49ers due to head trauma concerns - Niners Nation
How San Francisco 49ers' Chris Borland made his decision to retire over safety concerns - ESPN
Chris Borland slams Wisconsin football program in Netflix doc