How many millions did 49ers' Chris Borland give up by retiring at 24?
49ers' Chris Borland retires: NFL responds, cites safety progress
Chris Borland retiring out of concern for head injuries
Chris Borland Retires at Age 24 Over Concussions
49ers Linebacker Quits After 1 Season, Citing Safety Concerns
Chris Borland's Retirement Should Terrify The NFL. Here's Why.
Chris Borland retires from NFL at just 24 years old, makes his own
49ers ex-linebacker Chris Borland salutes Pat Tillman
Clarett on Chris Borland retirement: 'Lots of guys don't have a
How San Francisco 49ers' Chris Borland made his decision to retire
Another young NFL player calls it quits to protect future health
Another Shocker: 49ers LB Chris Borland retires at age 24
San Francisco 49ers rookie LB Chris Borland retires at age 24 over
Chris Borland retires: NFL must improve player safety - Sports
49ers LB Chris Borland retiring over concussion concerns