San Francisco 49ers linebacker Chris Borland retires over head injury concerns - ESPN
It's Time For East To Meet West In Sports Medicine, by Dr. Adam Gries
San Francisco 49ers Linebacker Retires At Age Of 24
In Andrew Luck's Retirement, Football's Consequences Weigh Heavily - The New York Times
Ex-49ers LB Chris Borland doesn't think football can be saved
NFL player's retirement at 24 prompts new debate about football concussions - The Washington Post
San Francisco 49ers Chris Borland retires over repeated head trauma
Another San Francisco 49ers player retires, Chris Borland retires due to safety concerns
First-game flaws too familiar for 49ers
Why is QB Alex Smith always traded when he has great success on whatever team he's on? - Quora
Chris Borland Retires from 49ers: Twitter Reacts to LB Retiring from NFL at 24, News, Scores, Highlights, Stats, and Rumors
49ers' Chris Borland Retires from NFL at Age 24