The incident happened just after 4 p.m. on State and Providence roads.
Two suspects are in custody, and the search continues for a third.
The undercover drug operation happened just a few blocks from the courthouse.
The Delaware County District Attorney's Office says ATF and county Drug Task Force agents were conducting an undercover drug operation at the Raven Motel in Media when two suspects fled in a SUV at a high rate of speed.
The ATF agent fired his weapon at the oncoming vehicle which hit him.
A pursuit began, and in the process of fleeing, the suspect's vehicle hit several cars.
The suspects ditched the SUV at the Blue Route on ramp at Baltimore Pike and ran into the woods.
"Investigators followed the vehicle, and eventually apprehend two suspects that were involved in the investigation, and one individual is being sought at this time by investigators," explained Stephen Bartholomew.
ATF agent was treated at a local hospital for minor injuries.
Police are currently searching for the third suspect. He is described as a heavy-set African American male with a beard wearing a lime green shirt.
Anyone with information is asked to contact police.