Quote from tradingjournals:
Some ore points are:
1. injury: visible by naked eye vs. by other means.
2. Physical cause vs. non-physical cause.
3. Intentional cause vs. intentional.
There are a lot of cases to discuss. Let us consider one you may have excluded so far.
Imagine a room full of people including some older people with weak legs, and some nut decides he wants to exercise what he think is his right to speech, and utter the word: "fire".
Imagine there is a stampede, and there are injuries. I would say the nut has caused injuries, yet the nut would tell me he is entitled to his speech, and it is not written anywhere that he cannot utter the word?
This has been covered by the USC:
The Schenck case
Holmes, writing for a unanimous Court, ruled that it was a violation of the Espionage Act of 1917, (amended with the Sedition Act of 1918), to distribute flyers opposing the draft during World War I. Holmes argued this abridgment of free speech was permissible because it presented a "clear and present danger" to the government's recruitment efforts for the war. Holmes wrote:
The most stringent protection of free speech would not protect a man falsely shouting fire in a theater and causing a panic. [...] The question in every case is whether the words used are used in such circumstances and are of such a nature as to create a clear and present danger that they will bring about the substantive evils that Congress has a right to prevent.
Holmes wrote of falsely shouting fire, because, of course, if there were a fire in a crowded theater, one may rightly indeed shout "Fire!"; one may, depending on the law in operation, even be obliged to. Falsely shouting "Fire!" in a crowded theater, i.e. shouting "Fire!" when one believes there to be no fire in order to cause panic, was interpreted not to be protected by the First Amendment.
The First Amendment holding in Schenck was later overturned by Brandenburg v. Ohio in 1969, which limited the scope of banned speech to that which would be directed to and likely to incite imminent lawless action (e.g. a riot). The test in Brandenburg is the current High Court jurisprudence on the ability of government to proscribe speech after that fact. Despite Schenck being limited, the phrase "shouting fire in a crowded theater" has since come to be known as synonymous with an action that the speaker believes goes beyond the rights guaranteed by free speech, reckless or malicious speech, or an action whose outcomes are blatantly obvious.
http://en.wikipedia.org/wiki/Shouting_fire_in_a_crowded_theater