1749-51 Mass. Acts 339, An Act for Preventing and Suppressing of Riots, Routs and Unlawful Assemblies, ch. 12.

"Whereas the Provision already made by Law has been found insufficient to prevent Routs, Riots, and tumultuous Assemblies, and the evil Consequences thereof :      Wherefore, 

Be it enacted by the Lieutenant Governour Council and House of Representatives, That from and after the Publication of this Act, if any Persons to the Number of Twelve or more, being Arm’d with Clubs or other Weapons, or if any Number of Persons consisting of Fifty or upwards, whether armed or not, shall be unlawfully riotously or tumultuously assembled; any Justice of the Peace, Field-Officer or Captain of the Militia, Sheriff of the County or Under-Sheriff, or any Constable of the Town, shall among the Rioters, or as near to them as he can safely come, command Silence while Proclamation is making, and shall openly make Proclamation in these or the like Words,

Our Sovereign Lord the KING, chargeth and commandeth all Persons, being assembled, immediately to disperse themselves, and peaceably to depart to their Habitations, or to their lawful Business, upon the Pains contained in the Act of this Province made in the twenty-fourth Year of His Majesty King GEORGE the Second, for preventing and suppressing of Riots, Routs, and unlawful Assemblies. GOD save the King.

And if such Persons so unlawfully assembled, shall after Proclamation made, not disperse themselves within one Hour, it shall be lawful for every such Officer or Officers and for such other Persons as he or they shall command to be assisting, to seize such Persons, and carry them before a Justice of Peace: And if such Person shall be killed or hurt by Reason of their resisting the Persons so dispersing or seizing them, the said Officer or Officers and their Assistants shall be indemnified and held guiltless..."