This is the 12818th most frequent Russian word.
кулаком
"Кулаком" means "with a fist" in English.
Here, 'кулаком' (with his fist) is used to describe the physical act of hitting something using the fist, specifying the instrument of the action.
Он ударил по столу кулаком.
He hit the table with his fist.
In this sentence, 'кулаком' (with my fist) is used figuratively to symbolize using physical force or intimidation as a means of persuasion.
Говори, а то я тебе кулаком покажу!
Speak up, or I'll teach you with my fist!
Here, 'кулаком' (fists) is used metaphorically to refer to physical violence or force in general, presenting the concept of resistance against it.