Learn how the 2002 death of one of football’s greatest linemen helped bring to light a rare disease, chronic traumatic encephalopathy, in this video from FRONTLINE: League of Denial. In 1991, "Iron Mike" Webster retired after 17 years in football and thousands of hits to his helmet. Soon after, he and his family suspected that playing football had taken a devastating toll on his brain. After Webster died, pathologist Bennet Omalu examined Webster’s brain tissue. His findings suggested that repetitive brain trauma causes an abnormal protein ("tau") to accumulate in the brain. This was the first evidence that playing football could cause a progressive neurodegenerative disease that results in permanent brain damage. This resource is part of the FRONTLINE Collection.