폭력적이다 means "violent" used for anything related with violence 난폭하다 means "rude; rough; cruel" used for a person or someone's action 격렬하다 means "intense; acute; fierce" used for argument or action like debate, battle, sports For example, 폭력적인 사람(O) 난폭한 사람(O) 격렬한 사람(X) 폭력적인 논쟁(X) 난폭한 논쟁(X) 격렬한 논쟁(O)