The best athletes to retire in their prime
49ers' Chris Borland retiring at 24, wary of head trauma – The Denver Post
PFF All-Decade Top 101: The best NFL players from the 2010s, NFL News, Rankings and Statistics
Former Ole Miss star Patrick Willis expected to retire from 49ers
A guideline for success in the NFL draft – The Denver Post
Bleacher Report - San Francisco 49ers make it official: Patrick Willis will retire. Details
49ers' Patrick Willis retires after injury-shortened season
Patrick Willis' Shock Retirement Marks Official End of Jim Harbaugh-Era 49ers, News, Scores, Highlights, Stats, and Rumors
Patrick Willis retiring from 49ers after injury-shortened season, NFL
Patrick Willis Explains Decision to Retire from NFL
49ers' Patrick Willis retires after injury-shortened season