The phrase "literal bang" means something is actually happening or occurring explosively, as opposed to using the word "bang" figuratively to describe a sudden impact or surprise. Full definition
Kicking off with a literal bang, a team of police officers force open the door of a flat in France, and with masks over their mouths, they walk around the apartment, open the windows and finally find what they're looking for. (indiewire.com)
However, the filmmaker never truly and fully explained the detective and criminal's relationship with each other; having started the movie with a visual and literal bang, as Max and Jacob fire their weapons at each other during a high - stakes robbery, Creevy doesn't satisfactorily elaborate on how the detective became involved in the case, or how Jacob is connected to the scandal within the police department. (shockya.com)