If you bang a part of your body, you accidentally knock it against something and hurt yourself. She'd fainted and banged her head He hurried into the hall, banging his shin against a chair in the darkness. Bang is also a noun. a nasty bang on the head
To beat or thump, or to cause (something) to hit or strike against another object, in such a way as to make a loud noise; as, to bang a drum or a piano; to bang a door (against the doorpost or casing) in shutting it
a fringe of banged hair (cut short squarely across the forehead) a sudden very loud noise the swift release of a store of affective force; "they got a great bang out of it"; "what a boot!"; "he got a quick rush from injecting heroin"; "he does it for kicks"