Dance documentaries can be insufferably dry and mannered, but this profile of Sergei Polunin, “the bad boy of ballet,” uses Black Sabbath’s “Iron Man” for an opening sequence in which the young Ukrainian dancer broods in his dressing room and then explodes onstage. Home-video footage allows director Steven Cantor to trace Polunin’s physical and artistic development from age eight, when he took up ballet, through his teen years, when his family fractured so that he could study in Kiev and later join the Royal Ballet in London. Polunin became the company’s youngest-ever principal dancer at 20, then shocked the dance world 18 months later by quitting; he has since reemerged in Russian ballet and as star of a viral dance video called “Take Me to Church.” Cantor attributes Polunin’s emotional turmoil to professional pressure and trauma over his parents’ divorce; like Amy, Asif Kapadia’s profile of singer Amy Winehouse, the movie shows a young person being dragged into adulthood by his own outsize talent. In English and subtitled Russian and Ukrainian.