Police say they arrested 23-year-old Ahmed Kromah on an assault charge Saturday night.
The alleged assault happened around 7:15 p.m. on Wednesday at the 174th-175th Street Station in the Mount Hope section.
Police said Kromah punched the woman in the face and then ran away down a set of stairs to leave the station.
They said the victim had no interactions with him before the incident.
The woman was taken to Bronx Care Hospital, where she was treated for pain and swelling.