The man, 21, and a friend were firing paintball guns at each other when another man with a real gun returned fire from across the street, a spokesman for the Chicago Police Department said.
The man with the paintball gun was hit in the right shoulder and taken to a local hospital.
The Chicago Sun-Times reported the shooter was arrested. The newspaper said the wounded man was also arrested because of an earlier incident in which he was suspected of firing the paintball gun at other people.
Media reports did not name either the shooter or the person who was shot.
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