In an interview, Myrna Loy stated that Max Baer carefully watched Primo Carnera's boxing style during the filming and used this information to beat him in their real-life match for the title in March, 1934.
The movie was banned by the Nazi government of Germany because Max Baer was Jewish. When asked about it, Baer joked, "They didn't ban me because I was Jewish. They banned me because I knocked out Max Schmeling in the ring."
Primo Carnera was the world's heavyweight boxing champion when this film was made and released. He refused to make the movie using the first script, which had him knocked out in the end, but agreed to a revised script with an additional $10,000 salary.
Jack Dempsey plays himself in the improbable capacity of a referee in the climactic fight. While giving the fighters instructions, he places unusual emphasis on the rule that requires the standing fighter to go to a neutral corner in the event of a knockdown. This undoubtedly is an allusion to the famed Long Count. In a 1927 title match, Dempsey knocked Gene Tunney down in the seventh round, but failed to go to a neutral corner immediately, which caused the referee to delay the count. Tunney recovered and won the fight.