According to Stacy Keach, Sixto Rodriguez knocked him out during their fight scene and that shot appears in the film.
The meaning and relevance of the film and source novel's 'Fat City' title is, according to a 29th August 1969 LIFE magazine interview by Michael Durham with the film's source novelist Leonard Gardner, as follows: "Lots of people have asked me about the title of my book. It's part of Negro slang. When you say you want to go to 'Fat City', it means you want the good life. I got the idea for the title after seeing a photograph of a tenement in an exhibit in San Francisco. 'Fat City' was scrawled in chalk on a wall. The title is ironic: 'Fat City' is a crazy goal no one is ever going to reach."
John Huston initially wanted Marlon Brando to play the role of Tully. When Brando informed Huston repeatedly that he needed some more time to think about it, Huston finally came to the conclusion that the star wasn't really interested and looked out for another actor until he finally cast the then relatively unknown Stacy Keach.
John Huston originally wanted Beau Bridges to play Ernie, but the actor felt he was too old. He recommended his own brother, Jeff Bridges for the part.
Reportedly, after a showing of this movie, champion boxer Muhammad Ali apparently said to the film's director John Huston: "Man that's for real, that's me talking up there."