Cappleman was hit by a blunt object around 7:15 p.m. at the corner of Racine and Leland.
He was not seriously hurt and refused medical treatment. One person was taken into custody by police.
Cappleman said that he had gone to the corner to check on a drunken disturbance at the corner.
"I know the individual who assaulted me. I have sat with him numerous times to help him address his addiction issues that have also led to him being without a job and a home," Cappleman said in a statement. "I continue to push for interventions that get people the real help they need."
Cappleman said that while it's important to be compassionate to the needs of the addicted, it is also important to recognize that the disruptive behavior that's become more common at this corner can be frightening to residents.
"The community suffers when this type of behavior takes over a street corner," he said. "Many residents who live near the intersection of Leland and Racine do not feel safe walking down the sidewalk."