Typically, boxing films are all about the flashbulb-popping, rope-a-dope climactic confrontation capping them off. So here, debut director Christopher M Anthony proves himself a contender by coming up with a new take: a pugilism flick that charts, in real time, the behind-the-scenes buildup to the showdown. Jordan Bolger plays “Diamond” Derek Douglas, drafted in on a wildcard to fight the current champ. But his preparations are jolted when his camp learns that Derek’s former training partner Cain (Osy Ikhile) has thrown his lot – and his insider knowledge – in with the enemy.

The boxing-movie genre is hardly short on self-destructive sluggers, but Anthony cranks up this exploration of mental fragility by hemming Derek into the locker room for the film’s duration. He suspects stalwart trainer Adam (Nicholas Pinnock) of being in cahoots with Cain and begins compulsively dialling his brother, a former fighter who once blew his own big shot. Punching a mirror in frustration isn’t exactly the stuff winners are made of, forcing Adam to conceal Derek’s injured hand. But, with camera crews, celebrities and firebrand promoter Freddie (Jason Isaacs) hovering, the underdog has to make like it’s no big thing.

Ducking and diving restlessly as he does with his camera around Derek and his team, Anthony’s nimbleness on the page becomes even more critical. He remains fully in sync with the interdependent dynamics between fighter and coach, with the in-crisis Derek alternately lashing out at Adam while looking at him for reassurance; the latter, meanwhile, has the fight of his life on his hands to find the right words and get his man in the ring. Bolger (looking more than plausible physically) and Pinnock both do incisive work fleshing out these psychological shifts.

Occasionally, as is sometimes the way with one-location or one-take dramas, Heavyweight forces story beats and labours for momentum. Relating much of the backstory verbally takes out some of the heat. And would Team Douglas really allow the turncoat Cain to spend so much time in the room sapping their boy’s confidence? But these are just quibbles; overall, this is a shrewd probing of the pressure-cooker environment of modern combat sports.

Heavyweight is in UK cinemas from 23 January