Police said a suspect approached another man riding on a Red Line train early Sunday morning near the North/Clybourn station.
The suspect was allegedly yelling and swearing before punching the victim and robbing him, Chicago police said.
Investigators say the victim followed the suspect off the train, where police say he was punched again.
No arrests have been made as CPD continues to investigate.
Following a number of recent incidents of violence on the CTA, a group of pastors prayed outside the Forest Park CTA Blue Line station on Wednesday. The effort was organized by violence prevention advocate Tio Hardiman.
The faith leaders and street outreach professionals then got on trains to promote peace in the public space and pray with riders.