Luke Kuechly Joins N.F.L.'s Under-30 Retirees Club - The New York Times
Chris Borland retiring out of concern for head injuries
NFL star Chris Borland quits over head injury concerns - CBS News
49ers ex-linebacker Chris Borland salutes Pat Tillman
Andrew Luck and Other Top NFL Players Who Retired Too Early, News, Scores, Highlights, Stats, and Rumors
The NFL Challenge: Keeping Gladiators Safe - The Atlantic Sponsor Content
Ex-49er Chris Borland still asked why he quit — and he keeps explaining – East Bay Times
Chris Borland Retires at Age 24 Over Concussions
How former San Francisco 49ers Chris Borland's retirement could change NFL forever - ESPN
Is Chris Borland's retirement the beginning of the end for the NFL? (updated) - The Washington Post