Concussion joins the small collection of investigative films arriving at the end of 2015, with Spotlight and Truth and the German picture Labyrinth of Lies. This one might actually move the needle on its subject. The true story chronicled here looks at Dr. Bennet Omalu, the Nigerian-born forensic pathologist who established a connection between football and Chronic Traumatic Encephalopathy, or CTE. That research has already led to changes in NFL rules and increased scrutiny of former players. All those shots to the head, all those concussions—acknowledged or, frequently, not—have created a class of ex-players struggling with depression, erratic behavior, and memory loss.