As most famously described by Justice Oliver Wendell Holmes in Schenck v. United States, "The most stringent protection of free speech would not protect a man in falsely shouting fire in a theatre and causing a panic." Other types of speech by individuals also fall outside the protection against prior restraint, including fighting words and obscenity.
"There are two ways in which the government may attempt to restrain speech," wrote scholar Henry Cohen in "Freedom of Speech and Press: Exceptions to the First Amendment" (Congressional Research Service, 2001). "The more common is to make a particular category of speech, such as obscenity or defamation, subject to criminal prosecution or civil suit, and then, if someone engages in the proscribed category of speech, to hold a trial and impose sanctions if appropriate. The second way is by prior restraint; i.e., to issue a court injunction against engaging in particular speech " publishing the Pentagon Papers, for example."