"Heckler's Veto": Two Related Meanings
There's been lots of talk recently about "heckler's vetoes"; I thought I'd note that this phrase actually has two different meanings, with different legal significance, though they are related.
[1.] Most commonly, "heckler's veto" refers to (to quote Black's Law Dictionary), "The government's restriction or curtailment of a speaker's right to freedom of speech when necessary to prevent possibly violent reactions from listeners." Here's an early reference from the Supreme Court (Brown v. Louisiana (1966)):
Participants in an orderly demonstration in a public place are not chargeable with the danger, unprovoked except by the fact of the constitutionally protected demonstration itself, that their critics might react with disorder or violence. See Cox v. Louisiana; Wright v. Georgia; cf. Terminiello v. Chicago…. See generally on the problem of the "heckler's veto," Kalven, The Negro and the First Amendment, pp. 140-160 (1965).
Generally speaking, such a heckler's veto violates the First Amendment, because it involves the government restricting speech based on its communicative effect (and the potential "disorder of violence" stemming from listeners' reactions to that effect). By extension, one can imagine a similar heckler's veto at, say, a private university, with the university stopping a speech because of the threat of attack by objectors to the speech. That wouldn't violate the First Amendment, but I think it's inconsistent with academic freedom principles.
[2.] "Heckler's veto" could also refer to a more direct form of suppression: Again to quote Black's Law Dictionary, "An interruptive or disruptive act by a private person intending to prevent a speaker from being heard, such as shouting down the speaker, hurling personal insults, and carrying on loud side-conversations." (See, e.g., Harcz v. Boucher (W.D. Mich. 2021).)
Such a heckler's veto doesn't itself violate the First Amendment, because it involves solely nongovernmental action (e.g., shouting down a speaker). Indeed, if it's limited to noise, it might not be civilly actionable in many situations, since interrupting speech isn't itself a tort. It can, however, sometimes be a crime, a form of disturbing the peace; for more on this, see here.
And institutions, public and private—such as universities—may well set up their own rules, forbidding this second kind of heckler's veto. If imposed and enforced in a neutral way, those rules don't violate the First Amendment or, I think, academic freedom principles. There is no right to interrupt a speaker who has been invited to give a speech in a way that keeps him from being heard, just as partisans of that speaker have no right to interrupt a speaker from the opposite side.
Of course it's unsurprising that the phrase has these two related senses, as so many words and phrases do (both in ordinary English and in legal jargon). Both involve hecklers (and potentially by extension people who go beyond heckling to physical attack) preventing speakers from speaking. In the second, the prevention is direct; in the first, the prevention operates through the extra step of government officials physically stopping the speaker, or threatening the speaker with arrest or prosecution. Still, the two meanings are somewhat different, especially for legal purposes.