UFC Hall of Famer Stephan Bonnar was arrested for DUI on Sunday -- after a group of concerned citizens (one armed with a gun) corralled him after an apparent car crash in Nevada.
Law enforcement sources tell us ... witnesses claim the 41-year-old was driving erratically and feared he would hurt someone.
Somehow, a group of concerned citizens wrangled Bonnar to the ground and kept him at bay until law enforcement arrived.
One he was taken into official custody he was booked for DUI, resisting arrest and unsafe driving. Bail was set at $22,000.