Learn about NFL player Chris Borland, who retired after just one season due to his concern about concussions, and why his decision prompted one media outlet to call him "the most dangerous man in football," in this video from FRONTLINE. [6:09] Borland left professional football, the game he loved since childhood, after reading about the effects of repeated head contact on the brain and speaking with a leading brain scientist. In response to the young star's headline-making retirement decision, NFL commissioner Goodell stated the game was safer than ever. Estimates from actuaries hired by the NFL state that three out of ten NFL players will have brain damage in their lifetimes. For background, watch Introduction to CTE and review How CTE Affects the Brain. Download teacher support materials for this resource: Teaching Tips, Video Transcript.