Why early NFL player retirements actually make sense
49ers' Patrick Willis will play vs. Eagles (w/video)
NFL star Chris Borland quits over head injury concerns - CBS News
Willis out, Smith in for 49ers' defense
Watch From Tackles to Tech: Patrick Willis' New Position - Bloomberg
Hanging It Up: Retirement Is the Latest NFL Trend
Luke Kuechly Joins N.F.L.'s Under-30 Retirees Club - The New York Times
Training camp roundup: 49ers linebacker Patrick Willis has 'slight' fracture in right hand
49ers hit hard after unexpected offseason departures - The Boston Globe