49ers rookie Chris Borland retires - The Boston Globe
Chris Borland's abrupt departure jolts the NFL
49ers' Chris Borland, 24, retires because of brain injury concerns
49ers' Chris Borland, 24, quits NFL over concussion worries
Chris Borland Retires: NFL Says Football 'Has Never Been Safer'
Chris Borland retires from NFL at just 24 years old, makes his own
Another young NFL player calls it quits to protect future health
San Francisco 49ers Linebacker Retires at 24 Over Head-Trauma Fears
Video Chris Borland Says NFL Career 'Not Worth the Risk' - ABC News
49ers' Chris Borland retires: NFL responds, cites safety progress
Chris Borland talks 'early' retirement in UW-Madison guest lecture
NFL player Chris Borland retires after one season at age 24 due to
NFL: Chris Borland retiring at 24, wary of head trauma
NFL star Chris Borland quits over head injury concerns - CBS News
Former Badger returns home with a mission