Will Smith plays Nigerian-born neuropathologist Dr Bennet Omalu, who first revealed the grievous damage a lifetime of head-pounding collisions did to American football players.

Unsurprisingly, his discovery of CTE (chronic traumatic encephalopathy) didn’t go down well with the multi-billion-dollar National Football League, which pulled out all the stops to discredit his findings.

When it focuses on this David versus Goliath battle, the film is genuinely gripping and stirring, with striking supporting turns by Alec Baldwin, Albert Brooks and David Morse as figures caught up in Omalu’s struggle.

But the film proves shakier when it tries to shoehorn elements of love story and thriller into its plot. Omalu’s romance with the young Kenyan woman who became his wife, Prema Mutiso (an underused Gugu Mbatha-Raw), feels sketchy, while scenes of shadowy stalkers seem to belong to a different movie entirely.