League of Denial: The NFL's Concussion Crisis

In a deposition, secretive billionaire hedge fund manager Steven Cohen struggles to answer this question.

The National Football League, a multibillion-dollar commercial juggernaut, presides over America’s indisputable national pastime. But the NFL is under assault as thousands of former players and a host of scientists claim the league has covered up how football inflicted long-term brain injuries on many players. FRONTLINE investigates: What did the NFL know, and when did it know it?

Pittsburgh Steelers center Mike Webster's favorite weapon was his head—and the hits kept on coming, for 17 years. In this excerpt from FRONTLINE's "League of Denial," Webster's peers describe what it was like to square off with "Iron Mike." Webster was diagnosed with chronic traumatic encephalopathy (CTE) after his death at age 50 in 2002.

In this clip from FRONTLINE’s League of Denial, neuropathologist Dr. Ann McKee discusses the brain of Penn football player Owen Thomas, who took his own life at age 21. After Thomas’s death, McKee conducted research on his brain and was shocked to find Chronic Traumatic Encephalopathy in the young defensive end.

NFL sensation Chris Borland was known as a fearless player, but after just one season he retired because he was afraid of head injuries. Now, Borland is known as the most dangerous man in football, a powerful voice in the NFL's growing concussion crisis.