A 20-year-old man was at the Harrison Red Line El platform late Wednesday night when a group of men approached and struck him in the face.
Police say they pushed the victim to the ground and took his wallet and iPhone before running away.
The Guardian Angels who were patrolling South Loop CTA stations Wednesday night following a shooting at the Roosevelt stop earlier this week saw what was going on and helped track down the suspects.
Four people are in custody, but charges have not yet been filed.
