Chicago police say the incident started when an off-duty officer saw people in two vehicles shooting at each other in the 300-block of South Leavitt.
The officer followed one vehicle to Van Buren and Oakley, where one of the men allegedly pointed a gun at the officer. That officer fired his gun, hitting the man.
The men took off and abandoned their car in the 300-block of South Maplewood.
The man with a gunshot wound was found nearby and taken into custody.