While the tracks were recorded separately the staged performances, the actors and actress actually performed their songs. Anton Yelchin and Alia Shawkat already knew how to play their instruments, but according to Jeremy Saulnier, Callum Turner had no experience with any sort of music. Joe Cole also learned to play drums, specifically for this movie.
Sir Patrick Stewart said in an interview that when he finished reading the script at his country home in England, it was so terrifying, that he locked up his house, turned on the security system, and poured himself a Scotch. He then knew that he wanted to play the Darcy Banker role because a character that horrifying would be an incredible challenge, and make for a compelling movie.
Red bootlaces are mentioned a couple of times, once in reference to people who were allowed to know what was going on, and once when a character earns their red laces. Red bootlace color is an important signal in skinhead culture indicating the wearer has shed blood for the skinhead movement. Racist skinheads will often randomly attack non-whites to "earn" their red laces.
The first song that the band plays at the skinhead club is a cover of the Dead Kennedys song, "Nazi Punks Fuck Off".