Fighting words are written or spoken words expressed to incite violence. This is related to the topic of hate speech, but it isn’t quite the same thing. Hate speech isn’t necessarily intended to incite violence (just simple hate in some cases).
In Chaplinsky v. New Hampshire (in 1942), the U.S. Supreme Court decided that “fighting words”, words that tend to incite an immediate breach of the peace, are among the
well-defined and narrowly limited classes of speech [which] the prevention and punishment of have never been thought to raise any constitutional problem. These include the lewd and obscene, the profane, the libelous, and the insulting or “fighting” words those which by their very utterance inflict injury or tend to incite an immediate breach of the peace.
Speech that merely causes anger, offense, insult or outrage does not amount to fighting words. Fighting words must present an actual threat of immediate violence or must “reasonably incite the average person to retaliate.”
It’s not true that certain words inevitably provoke violent reactions by individuals. Rather, one should take into account the context in which the words were uttered, not merely the content of the words themselves.
Given the rules for limiting free speech described in this post, the case of fighting words is rather simple. Inciting violence leads to violations of individual rights to security and bodily integrity, and in many cases these rights should take precedence over the right to free speech. It seems difficult to accept that hurting someone is a lesser evil than limiting someone’s right to speak and threaten.