Barry McGuigan coached Sir Daniel Day-Lewis for two years to prepare him for the boxing scenes. He was also a regular commentator at fights all over the country, and familiar with the form of most boxers. He said Day-Lewis was so good and so serious about his training that he could easily have contested real boxing matches against the leading fighters in his weight class at the time.
Although set in Belfast, the film was almost exclusively shot in the run-down docklands and Sheriff Street area of Dublin's North Inner City. The flat complex used in the film was earmarked for demolition but this was postponed until filming was completed. Since then the entire area has been redeveloped and now contains several multinational company headquarters, a college, hotels, up-market restaurants, a rail station and million dollar apartments.
The boxing match in the film, complete with the unusual result, was based on an actual bout.
Eddie Carroll is the name of a Canadian hall-of-fame welterweight boxer who fought in the 1930s and '40s.