This documentary portrait of professional hockey enforcers—the tough guys who duke it out to protect their team’s star players—also proves to be one of tragic self-destruction. Offering a historical and contemporary overview of NHL brutes, Alex Gibney’s gripping film fixates most squarely on notorious Montreal Canadiens roughneck Chris “Knuckles” Nilan. While often distractingly cutting away to detail the tales of other like-minded players, Gibney primarily focuses on Nilan’s rise to glory as a skater with a preternatural skill for fighting, which endeared him to Montreal fans but became a burden as age took its toll on his body, and unwanted trades to other teams sapped him of his once-ferocious passion. Blending archival footage and new interviews with Nilan, his family, journalists, and fellow combatants, Gibney celebrates hockey’s fisticuff traditions while also recognizing how such brutality ultimately takes its greatest toll on those who perpetrate it. Discussing his subsequent descent into drug addiction and crime, Nilan proves self-reflective and regretful about a promising life turned sour by an inability to function once his abilities, and career, ended. Compellingly likened to a soldier returned from war, he’s ultimately a case study in the difficulty of adapting, and changing, in order to survive.