In an interview, director Jack Cardiff said that only four minutes and five seconds of the footage shot by John Ford ended up in the finished movie. The riot scene was cited by critics as the obvious work of Ford, yet it was completely done by Cardiff who admitted that he found inspiration from Battleship Potemkin (1925).
The character of "John Cassidy" is allegedly based on playwright Sean O'Casey (his name is an Anglicization of O'Casey's), but Rod Taylor, playing the part, bears no resemblance to the famous writer. The real O'Casey was a diminutive man with poor eyesight who always wore thick glasses and kept out of violent encounters. He was a working-class man of strong intellectual gifts and fierce political views, and in reality was, at the time of the events depicted, about fifteen or twenty years older than "Cassidy" is supposed to be.
John Ford was keen on casting either Peter O'Toole or Richard Harris in the lead. Sean O' Casey, on whose early life this movie was based, suggested the less starry Donal Donnelly or Norman Rodway for the part.