Film Language Tag: nondiegetic insert
An insert that depicts an action, an object, or a title originating outside of the space and time of the narrative world.
Tyler Durden (Brad Pitt) encourages The Narrator (Edward Norton) to stay over at his place. Once that's settled he asks him to hit him. The Narrator then gives us a backstory for Durden. It flashes back to the present and The Narrator hits Durden, starting the first fight of the movie and the beginning of fight club.