49ers’ Chris Borland, Citing Safety, Is Latest to Retire Early From N.F.L.

Linebacker Chris Borland of the San Francisco 49ers, one of the top rookies in the N.F.L. last season, is the latest case yet, and perhaps the most noteworthy. He said Monday that he was leaving football because of concerns about his safety.

.. But Borland, 24, who played at the University of Wisconsin, is the youngest and most promising of the players to leave the N.F.L. this off-season.

“From what I’ve researched and what I’ve experienced, I don’t think it’s worth the risk,” Borland told ESPN.