During an action scene, Mel Gibson accidentally hit Frank Grillo in the face, dislocating his jaw. Grillo didn't let on as he didn't want to slow up the filmmaking process. 8 hours later, a medic was able to reset his jaw.
Joe Carnahan had been trying to make this movie for years. It was originally called "Continue" and was written by Chris Borey and Eddie Borey in 2010. Carnahan rewrote the script and announced in 2012 that he would direct it for 20th Century Fox. He later filmed screen tests with Frank Grillo. Fox ultimately decided not to move forward with it, reportedly disagreeing with Carnahan's choice to cast Grillo as the star. Carnahan later posted the screen tests on Twitter.
Roy tells Joe that Liam Neeson is a "fake tough guy." Neeson has worked with this movie's director Joe Carnahan before in The A-Team (2010) and The Grey (2011) (also with Grillo) and this quip was undoubtedly an inside joke between the three.