Director F. Gary Gray decided to use Del Frisco's Double Eagle Steakhouse as the restaurant that caters Clyde's lunch after dining there several times during filming. The restaurant was also the location of the film's after-party following its screening at the Philadelphia Film Festival.
Ironically enough, in real life, Gerard Butler studied law and was close to being a lawyer before becoming an actor
While Gerard Butler was originally signed and announced to play the role of Nick Rice, there are different stories about how Jamie Foxx took on that role and Butler was re-cast as Cylde Shelton. In one version, Foxx called the producers and asked if Butler would like to play Clyde Shelton instead, as he liked the role of Nick. When the producers approached Butler about playing Clyde, he thought about it for a second and reportedly said "Jamie as Nick... and me as Clyde? That would be awesome!" However, Butler also said in an interview that HE suggested the role switch between himself and Foxx via his role as a producer on the film. Butler also said that he initially regretted that this idea was implemented by the other producers, but added that the entire process worked out well for the project.
Gerard Butler's character uses the line "It's not what you know, it's what you can prove in court". This is the same line Denzel Washington uses in Training Day (2001) minus the "in court". It's actually Jamie Foxx's character who says this