An armed security guard at a Philadelphia gas station fired a single shot at a man who threw a softball-sized rock at him. The security guard was escorting the person off the premises for panhandling and harassing customers.

As the guard let the man away, he grabbed a large chunk of concrete and threw it toward the guard. In response, the guard pulled out his gun and fired a single shot, missing the man.

"We're not sure if it was a warning shot, we don't know that at this time until we interview both parties," Chief Inspector S cott Small told WTXF.

Andre Boyer, head of the private security company that employs the security guard, told the news station that the man had been harassing customers at the gas station the day before as well.

"The guy threatened him and threatened other people here, and he took self-defensive action," Boyer said, defending the actions of the guard.

Authorities arrested the rock thrower and charged him with simple assault and reckless endangerment. No charges have been filed against the security guard, but that could change as the investigation continues.

"It's going to be a very thorough investigation since deadly force was used, even though no one was shot, no one was even struck by gunfire, no one was even hit by a rock," Small said.