San Francisco 49ers linebacker Chris Borland has decided to retire from the NFL during the prime of his career because of concerns about the consequences of football-induced head trauma. The Nation’s sports editor Dave Zirin, joined MSNBC’s News Nation with Tamron Hall to discuss the significance of the 24-year-old’s decision to leave the game.

“Science is not the NFL’s friend,” Zirin said. “The more people know about the effects of tackle football, the more you’re going to see parents withhold their kids from playing and the more you’re going to see players make the kind of choice that Chris Borland is making.” Because a rising star like Borland was sure to receive a lucrative contract, Zirin argued, “he’s actually sacrificing something for the principle of his own health and that makes it a political act.”

James F. Kelly