Antoine Fuqua had no money to pay James Horner to compose the film, due to the film's short budget. However, Horner did not care as he loved the idea of the film, and he decided to do it for free.
Eminem was originally scouted for the role, which he accepted and started filming. The film had to be put on hold as Eminem wanted to focus on his music career, so the role was then given to Jake Gyllenhaal.
Some prints of the film, at the end of the credits, have "In Memory of Our Friend James Horner," who died in a plane crash days before the film opened for release.
This is the next to last film scored by composer James Horner, before dying in a plane crash on June 22, 2015. His last film in release, The 33 (2015), was released later in the year, his final score for the western remake The Magnificent Seven (2016), also directed by Antoine Fuqua, was released in September 2016.
The song that plays at the end of this film, "Wise Man" by Frank Ocean, was originally written to be in Django Unchained (2012). Quentin Tarantino wasn't able to find a scene to place the song in, so it was eventually scrapped from the final cut.