Massachusetts General Laws Part III. Courts, Judicial Officers and Proceedings in Civil Cases (Ch. 211-262) Ch. 220, § 3

The justices of the supreme judicial court and of the superior court, justices and special justices of district courts, by virtue of their offices, and justices of the peace shall be conservators of the peace throughout the commonwealth and as such may, upon view of an affray, riot, assault or battery, without a warrant in writing, command the assistance of every sheriff, deputy sheriff, constable and police officer and of all other persons present for its suppression and for the arrest of all persons concerned therein as provided in chapters two hundred and seventy-five and two hundred and seventy-six. Persons so arrested shall be taken before a district court or trial justice for examination.