Officers stopped three people in an alley in the 4400 block of North Mulligan.
They may have been breaking curfew.
The suspect, believed to be 16, ran away but got cornered in a gangway, where police say he swung a piece of fencing at an officer.
The suspect was taken to the hospital for non-life threatening injuries.
He reportedly told police he didn’t want his sister to know he was out after midnight.