Vigilantism

Vigilantism is the act of enforcement, investigation or punishment of perceived offenses without legal authority.
A vigilante (from Spanish and Italian "vigilante") is a practitioner of vigilantism.
History.
Vigilantism and the vigilante ethos existed long before the word "vigilante" was introduced into the English language. There are conceptual and psychological parallels between the Dark Age and medieval aristocratic custom of private war or vendetta and the modern vigilante philosophy.
Elements of the concept of vigilantism can be found in the Biblical account in Genesis 34 of the abduction and rape (or, by some interpretations, seduction) of Dinah, the daughter of Jacob, in the Canaanite city of Shechem by the eponymous son of the ruler, and the violent reaction of her brothers Simeon and Levi, who slew all of the males of the city in revenge, rescued their sister and plundered Shechem. When Jacob protested that their actions might bring trouble upon him and his family, the brothers replied "Should he [i.e., Shechem] treat our sister as a harlot?"
Similarly, in , Absalom kills his brother Amnon after King David, their father, fails to punish Amnon for raping Tamar, their sister.
In the Western literary and cultural tradition, characteristics of "vigilantism" have often been vested in folkloric heroes and outlaws (e.g., Robin Hood).
During medieval times, punishment of felons was sometimes exercised by such secret societies as the courts of the Vehm (cf. the medieval Sardinian "Gamurra" later become "Barracelli", the Sicilian Vendicatori and the Beati Paoli), a type of early vigilante organization, which became extremely powerful in Westphalian Germany during the 15th century.
Vigilantism in the United States of America.
Formally-defined vigilantism arose in America during Spanish rule.
After the founding of the United States, a citizen's arrest became known as a procedure, based in common law and protected by the United States Constitution where a civilian arrests a person whom they have seen or suspect of doing something wrong.
The exact circumstances under which this type of arrest, also known as a detention, can be made varies widely from state to state.