To take action to enforce the law or penalize someone without having the legal authority to do so

स्वयं न्याय करना

English Usage: Frustrated by the lack of police action, the villagers decided to take the law into their own hands.

Hindi Usage: पुलिस की कार्रवाई से निराश होकर गांववालों ने कानून अपने हाथ में लेने का फैसला किया।