Chicago police said the 33-year-old officer was attacked just before 3 a.m. in the 5100-block of South Kimbark Avenue.
Someone reportedly exited a black SUV and tried to rob him. After a struggle, the suspect left the scene.
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The off-duty officer suffered some minor scrapes and refused treatment, Chicago police said. His name hasn't yet been released.
Area One detectives are investigating. No one was in custody later Tuesday morning.