The unnamed guard, a 29-year-old man, was patrolling Dilworth Park just after 11: 30 p.m. on Monday, Feb. 13, when he asked a group of people to leave the area, police said.
The discussion escalated to a "physical altercation," during which a suspect pulled out a handgun and fired two shots at the guard, the department said.
The 29-year-old was uninjured, but the gunman fled the scene, police said. The case remains under investigation by the Central Detectives Division.
It's at least the second such incident at City Hall in recent memory. On Jan. 9, Philadelphia police shut down traffic in Center City after a gunman opened fire on 15th and Market streets.
Click here to follow Daily Voice Bristol and receive free news updates.