It happened at the Broadway-Lafayette station on Aug. 10 just before 8 p.m.
Authorities say the suspect punched the victim multiple times in the face, causing him to fall and his his head on the platform.
The victim was taken to the hospital with a cut to the head and swelling and bruising.
The suspect ran away in an unknown direction. He was last seen wearing a red and black jacket, black pants, white sneakers and pushing a hand truck.
Anyone with information is asked to call the NYPD's Crime Stoppers Hotline at 1-800-577-TIPS (8477) or for Spanish, 1-888-57-PISTA (74782).
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