The incident happened at the Elder Avenue subway station in the Bronx around 7 a.m.
The video shows a woman repeatedly punching a man.
The man reacts by dragging the woman off the train and starts kicking her in the stomach.
Investigators are working to identify the people involved.
Anyone with information is asked to contact the NYPD's Crime Stoppers Hotline at 1-800-577-TIPS (8477) or for Spanish, 1-888-57-PISTA (74782).
You can also submit tips by visiting the CrimeStoppers website at crimestoppers.nypdonline.org or by messaging on Twitter @NYPDTips.
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