CPD said a teenager grabbed a 69-year-old man's shoulder from behind and pushed him down the stairs at the Chicago stop in River North before running off.
The victim suffered minor injuries and detectives are now trying to identify the suspect.
The teen is described as 16-18 years old, 5-foot-6 to 5-foot-8, and between 150 and 170 pounds.
He wore a green and black-colored camo balaclava mask on the lower portion of his face, a black hooded sweatshirt, a dark-colored backpack, black pants, and grey gym shoes.
Police asked anyone with information to call them at 312-745-4447 or submit an anonymous tip at CPDTIP.com and use reference RD#JK-307232.
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