Tonight, Frontline (on PBS) airs a two-hour report about professional football and head injuries. The episode, "League of Denial: The NFL's Concussion Crisis," specifically addresses whether the NFL knew about the dangers of head injuries, and kept that information from players and, by default, fans of America's most popular spectator sport.

The controversial topic began here: It was Pittsburgh forensic pathologist Dr. Bennet Omalu who, in 2002, examined the brain of former Steeler Mike Webster, and found evidence of CTE (chronic traumatic encephalopathy), a degenerative condition. Interviewed by Frontline, Omalu said: "I saw changes that shouldn’t be in a 50-year-old man’s brains, and also changes that shouldn’t be in a brain that looked normal.”

The program airs at 9 p.m.