The incident happened last Sunday after 11 p.m. on Courtlandt Avenue in the Melrose section of the Bronx.
The NYPD released video of the attack, in which the suspect wound up and delivered a blow that knocked the victim off his feet before running away.
The 81-year-old victim suffered pain and bruising to the face and was taken to Lincoln Hospital in stable condition.
Police say there was no interaction between the victim and the suspect prior to the assault.
The suspect is described as a Hispanic male with curly black hair. He was last seen wearing a black shirt, black shorts and white sneakers.
Anyone with information in regards to this incident 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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