Christina Hendricks was cast alongside Naomi Watts and Liev Schreiber back in 2011 when the project was announced. Hendricks dropped out while the film was stuck in development and eventually Elisabeth Moss replaced her.
Liev Schreiber & Naomi Watts were a couple in real life, until they called off their engagement in 2016.
Was originally called "The Bleeder", but changed to "Chuck" due to viewers thinking it was a horror film, as well as other movies with the same name according to Chuck Wepner. In several European countries, the movie was still released as "The Bleeder", though.
James Brown sang in the ring before the Ali-Wepner fight and did a pre-fight performance on screen in Rocky IV.
Liev Schreiber, unlike his character Chuck Wepner, does have a role in the "Rocky" franchise. He assumes his real-life role as the narrator of HBO Sports Documentaries in the film "Creed", a spin-off of Rocky's saga.