Watch an exclusive clip from the new tennis doc

Tennis is in full swing at this year’s Toronto International Film Festival. With the US Open tournament in New York entering its final weekend, North America’s biggest movie jamboree is screening Battle of the Sexes (starring Emma Stone and Steve Carell as Billie Jean King and Bobby Riggs) and Borg/McEnroe (featuring Shia LaBeouf as the latter). But perhaps no one, even in those two films, represents a character as larger-than-life than famed, controversial former coach and prodigy-builder Nick Bollettieri.

Jason Kohn’s excellent documentary Love Means Zero — a fantastic pun of a title — presents itself initially as a biography of the garrulous, leather-skinned Bollettieri. Now 86 and living in Florida, where his boot camp tennis academy once pumped out champions (as you can see in the clip, above), the retired coach sits in a chair with a dilapidated court behind him. “You got to understand Nick, baby,” he yowls, speaking in the third-person. “Nick doesn’t look back, Nick only goes forward. If you asked me right now to give you the names of my eight wives, I couldn’t do it!”

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But Kohn presses on. It would have been easy, thanks to Bollettieri’s argumentative personality and hilarious bon mots, for the film to just be a surface-level chronicle of a successful eccentric. But Love Means Zero is an incisive, colorful portrait of one man’s pain, hubris, and reconciliation with his past. Taking focus as the film’s main subject is the surrogate father-son relationship between Bollettieri and his most famous pupil, Andre Agassi. Their partnership and subsequent breakup trace a haunting arc over the whole story — no less powerful for the fact that Agassi refused to participate in the film.

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“The documentary was originally a more straightforward look at the life of a tennis coach I remembered fondly from my childhood,” director Jason Kohn tells EW. “Then Agassi refused to sit down for an interview, and everything changed. I realized this wasn’t simply a historical film. It also had a strong present tense storyline. Though they parted ways over 20 years ago, Agassi and Bollettieri were both still hurt — and so my sports documentary evolved into a family drama.”

Love Means Zero premieres Sept. 8 at the Toronto Film Festival. Showtime plans to air the documentary next year.