Professional boxers played Jimmy Braddock's opponents. They were told to land their blows as close to Russell Crowe's body as possible. Unfortunately, they sometimes couldn't pull back in time and ended up injuring Crowe.
After the film's release many boxing analysts and even Max Baer's son, Max Baer Jr. decried the movie for its historical liberties taken with Max Baer. Specifically, that he had killed two men in the ring (he did kill one and an opponent he'd KO'd died a few weeks after their bout for reasons unrelated to the fight) and that he took pride in that fact. Max Baer Jr. has said that his father was always haunted by the memories of killing a man in the ring.
This Depression-era drama made headlines for being not only one of the best reviewed films of 2005, but one of the least well attended. After four weeks of release the film had taken around US$50 million, which even during the box-office slump of the time was a disappointment, especially considering the good buzz. AMC Theatres hoped to keep the film and started a unique offer of a money-back guarantee. Ticket buyers who did not like the film were promised that their money would be refunded, no questions asked.
Braddock's African-American corner man in the film as well as in real life was Joe Jeanette (played by Ron Canada). Jeanette himself was a top flight heavyweight contender during the 1900s to the 1910s, but never received a title shot, due to the racial climate of the time. He owned the New Jersey gym in which Braddock often trained.
The cinematographer invented a "tire-cam" which is a camera cushioned inside a tire and behind Plexiglas. This allowed the professional boxers to hit the tire to create realistic reactions from a first-person point-of-view.
Max Baer, who's paternal grandfather was Jewish, boxed with a Star of David embroidered on his trunks. The star is visible on Baer's red trunks throughout his fight with Braddock in the final fight scene.
The story Jimmy Braddock tells of his kids confusing the word "title" with the word "turtle" is true. A reporter asked Braddock's son Howard Braddock what he would do if his father brought home the title young Howard replied that he'd "play with it. Pull it around on a string".