First Amendment
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof, or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
Categories of speech that are given lesser or no protection by the First Amendment (and therefore may be restricted) include obscenity, fraud, child pornography, speech integral to illegal conduct, speech that incites imminent lawless action, speech that violates intellectual property law, true threats, and commercial speech such as advertising. Defamation that causes harm to reputation is a tort and also an exception to free speech.
Defamation is proven by showing five elements: A statement was made about you, The statement was false,
The statement was published, The statement harmed your reputation, and No privilege or defense exists for it.