Sylvester Stallone gained 40 pounds to add realism to his portrayal of the police officer. He also was only paid SAG minimum wages. By the time that reshoots were required, he had lost the weight again.
At the end of the film, when Freddy and Gary are bringing in Murray Babitch to the NYC authorities, there is one shot of Moe Tilden coming out of a building. In this one shot, his mustache is noticeably longer. Director James Mangold wanted to get a shot of Robert De Niro's character walking out of the building. De Niro had already completed his scenes and was already working on another film, Jackie Brown. De Niro agreed to return and appear in the shot, but could not trim his longer mustache as it was required for his character, Louis Gara, in Jackie Brown.
Robert Patrick got the part after running into actor Peter Berg and the film's producer and music supervisor, Meryl Poster, who were staying in the same hotel in New York. He got the script and then read for director James Mangold a few days later.