(a) A person is guilty of riot in the first degree when simultaneously with six or more other persons he engages in tumultuous and violent conduct and thereby intentionally or recklessly causes or creates a grave risk of causing public alarm, and in the course of and as a result of such conduct, a person other than one of the participants suffers physical injury or substantial property damage occurs.
(b) Riot in the first degree is a class A misdemeanor.