Charlie Hunnam wanted Tommy Flanagan, to play the role of his older brother, even going to a bar for three nights that he knew Flanangan frequented with a script in hand for him to read. They would later co-star on 'Sons of Anarchy'.
West Ham were approached by the film-makers who wanted to shoot scenes at their Upton Park ground. As they were under the impression that the film was celebrating the glorious game and its fanatical supporters, they agreed. Once they realized the film's true take on the subject (after filming had taken place), they disassociated themselves from the project.
The actors playing the Green Street Hooligans had to work out with the production's trainer for four or five hours every day. The trainer, Pat E. Johnson, had most of the actors throwing up, he was working them so hard. A typical day would involve basic strength and fitness training for about two hours, followed by choreographing of the fight sequences. Rehearsals would take place in the afternoon, and then in the evening they would all go out drinking (which is probably why most of them were throwing up the next day). Elijah Wood was absented from most of this rigorous schedule to emphasize his outsider status.
When hopping off the train at Macclesfield, as they are expected at Manchester and being waited for by the rival firm, it is not actually Macclesfield Station, but Westbury train station, in Wiltshire, a couple hundred miles away.