The 2001 Game Boy Advance game "Ecks vs. Sever" was actually based on an early script draft for this film and not the other way around. The game's producers later made a sequel to that game that was based on the finished version of the movie.
Started as a spec script by Alan McElroy in the mid-late eighties under the title 'Legion' which was later renamed 'Gunner'. In 1988, the project almost got made at Vestron Pictures with Dwight H. Little to direct and starring Dolph Lundgren but it got stopped with Charles W. Fries holding it up and not wanting to do it..
While filming a large-scale action scene that involved explosives, a detonation occurred that was too close to principal actor Antonio Banderas. As a result, Banderas was almost badly burned, but escaped with minor scorching. He allegedly was quite vocal with the FX team for their careless calculation of how big the explosion was going to be.