Complex sentence: It tells the story of Tim (played by Antoine Olivier Pilon), who joins his school's athletic programme to confront the bully Jeff Roy (played by Lou-Pascal Tremblay) who happens to be the star of the school's athletics programme.
Split into simpler sentences: It tells the story of Tim (played by Antoine Olivier Pilon), who suffers from bullying in school at the hands of Jeff Roy (played by Lou-Pascal Tremblay). Tim joins his school's athletic programme, to be able to confront the bully, the star of the school's athletics programme.