"Troll" is both a verb and a noun. Originally it was just a verb: "to provoke responses by metaphorically dragging bait", but it soon broadened to mean "somebody who provokes responses by metaphorically dragging bait". And in modern times the meaning has broadened still further to include direct insults, which is a needless loss of precision in language because there was already the perfectly good verb "flame" for that meaning . But even after all the extension of meaning, the origin of the word is still the dragging of fishing bait.