There's some irony here: The man who maybe has done the most to bring a hot-button issue to public attention - the later-life dangers from repetitive football hits - isn't in the film that will give the issue its greatest public attention.
The first thing I did on hearing Concussion the film was coming out was to check the cast list, to see who was playing Chris Nowinski.
Answer: nobody.
Obviously, storytelling requires tough decisions to keep the story moving. Concussion spotlights a crucially important figure in this whole saga, Bennet Omalu, the Pittsburgh pathologist then working at the Allgeheny County coroner's office who had studied the brains of two deceased NFL stars and found massive trauma.