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.
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.
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 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".
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.
Before Damon Runyon gave Braddock his nickname, the term "Cinderella man" was considered an insult similar to the use of "gigolo" today. A Cinderella man was a downtrodden man who met and married a rich "Princess Charming" in the same way that Cinderella met and married Prince Charming. A Cinderella man was also considered to be less than a true man, as he allowed his wife to fund their lifestyle. An example of this occurs in the movie Platinum Blonde (1931): When the male lead is called a Cinderella man to his face, he punches the man and tells the man that he wears the pants in the marriage.
In the actual Baer fight, Braddock was introduced last. Which is not traditional (the champion is introduced last). But he was the sentimental choice. The local hometown underdog fighter. Baer from California was introduced first to polite applause.
Art Binkowski (Corn Griffin) didn't like being knocked down during the Griffin/Braddock fight scene. He'd never fallen in a real fight, and he didn't want his opponents to think it was even remotely possible.
The trivia item below may give away important plot points.
Rance Howard, who portrayed the ring announcer and is the father of fellow actor Clint Howard and actor/director Ron Howard, attended the fight in which Jim Braddock won the heavyweight title with his father. Considering he was in Oklahoma during the Depression it is unlikely he attended the fight in New York. Here is probably what happened: Howard's grandfather took Howard's father to a pool hall to listen to the Braddock/Baer fight on the radio. It was the first boxing match his father had ever heard. Now he's a life-long fan.