The footage, shot from the sidewalk, shows several officers surrounding a young male on the hood of a car, the New York Daily News reported on Friday.
Suddenly, what appeared to be a plainclothes officer ran into frame and began punching the young male as the other cops continued to press him against the car.
"Hey, hey, hey stop it! Get off of him!" a woman outside of the shot shouted.
"He's 12! Why did you just do that?" another woman is heard saying to the police. "I'm a lawyer, I can't believe you just did that."
The crowd continued to confront the police over the course of the 8-minute video, which eventually showed another young man against the hood of a different car complaining and shouting at the cops.
NYPD Internal Affairs was investigating the episode, police told the paper.
Police said the two were arrested for assaulting someone with a cane. The date of the apparent assault remains unclear.