It happened just before 8 p.m. Tuesday on the platform at East 170th Street and Jerome Avenue.
Police say a man was stabbed and taken to Lincoln Hospital.
He's in stable condition.
Police are asking for the public's help tracking down the suspect.
Call 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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