Chris Borland Speaks Out on Why He's Quitting the NFL

— -- San Francisco 49ers rookie linebacker Chris Borland's surprise announcement that he will be retiring at the tender age of 24 has caused a stir in the NFL.

Borland, 24, told ESPN earlier this week that he made his decision after consulting with those close to him and studying what is known about the relationship between football and neurodegenerative disease.

Chronic traumatic encephalopathy (CTE), a degenerative brain disease, has been linked to repeated head trauma experienced by National Football League players and other professional athletes who report a high rate of concussions and sustain repeated blows to the head.