The incident happened around 2:30 a.m. Sunday morning on Bowery Street on the Lower East Side.
Surveillance video shows a man attack 23-year-old Kyle Rogers, of Rockville Centre, from behind as he was walking down the street.
Another man can be seen on the video recording the whole thing.
Rogers suffered a broken jaw, which had to be wired shut. He was unconscious for several minutes before being taken to Bellevue Hospital
"I had no defense at all," he told Eyewitness News reporter NJ Burkett. "You shouldn't have that fear always in the back of your head, oh someone's going to come out nowhere and punch me."
He believes it was the latest in a string of knockout attacks in New York City.
"It's cowardly, you know?" he said. "If you're going to face me face to face, and punch me like that, that's one thing. But to run up from behind me? It's like, c'mon."
Surveillance video has caught similar attacks over the last several months, all of which are seemingly random and don't appear to be attempted robberies.
A similar but unrelated attack happened the same day in Vinegar Hill, Brooklyn.
Anyone with information is asked to call Crime Stoppers at (800) 577-TIPS (8477).