(formerly in England) a statute of 1715 by which persons committing a riot had to disperse within an hour of the reading of the act by a magistrate
2. read the riot act to someone
Riot Act in American English
an English law, passed in 1715, providing that if twelve or more persons are unlawfully assembled and disturbing the public peace they must disperse on proclamation (reading the Riot Act) or be held guilty of felony