Terminiello v. City of Chicago

Father Terminiello (defendant) gave a controversial speech that drew angry protesters and disturbances outside a Chicago auditorium, and the City (plaintiff) prosecuted him under an ordinance banning speech that stirs the public to anger, invites dispute, or creates unrest; Terminiello raised no objection to the jury instruction based on that ordinance language at trial, was convicted, and both Illinois appellate courts affirmed.

Whether free speech is constitutionally protected unless it is likely to produce a clear and present danger of a serious substantive evil beyond public inconvenience, annoyance, or unrest.