Police said the man first tried to fire a gun but it malfunctioned, then pulled a knife, triggering the confrontation with the guard.
Authorities said the man was from out of state, was not listed as a defendant or plaintiff in court records, and investigators found nothing threatening in his parked vehicle.
The courthouse front entrance closed, most employees sheltered in place, and the building and nearby Nashville Public Library were evacuated as the FBI, U.S. Marshals, Nashville police and Tennessee investigators joined the case.