Authorities say an officer was off duty and not in uniform when he stopped to help at a traffic accident near Armitage and Kilbourn at approximately 10:30 p.m.
According to police, a man at the scene was acting irrationally and tried to open the officer's car door while reaching across his body into his waistband.
That's when police say the officer fired a shot.
The man was shot in the hand and was under arrest Wednesday.