After a clash involving police is caught on video, an NYPD officer named Risel Maritnez has been placed on modified duty. NY1 Criminal Justice Reporter Dean Meminger reports that witnesses say they can't believe how violent the officer was.

A chaotic scene inside a Harlem building. Residents say a plainclothes officer was so hyped up, he beat and arrested two men and pulled his gun on people videorecording the arrest.

Calvin West was one of the people recording when the officer pulled out his gun.

Meminger: Were you trying to help the guy who was being arrested?
West: None at all. There was no need at all. All I was doing was recording an unlawful crime. That's it
Meminger: So you think what the cops were doing, you think they were unlawful, the cops?
West: They were unlawful. They were unlawful.

The NYPD says they were doing a car stop when some people on motorized dirt bikes started circling them.  Authorities say when they went to approach the riders, they took off. Police say the car's driver fled on foot.

Later, authorities say officers encountered one rider at a building on 134th Street and Eighth Avenue and arrested him. Witnesses say he didn't resist but allege he was still beaten by police.

"Put his hands up, 'I don't want no problems.' Cop punched in his face about three or four times, slammed him on his head," West said. "That's when I got the camera out."

"He didn't pull the gun out like this here. He held the gun out like he was one of them God damn gangsters or like a gang member, you know, and saying, 'Get away, get away,'" said tenant association president Deloris Johnson.

Then, there's video of the same plainclothes officer punching someone else recording the situation.

Community activists say for them, this is another example of officers trying to prevent people from legally videotaping police activities.

"I think a lot of officers are starting to react again like they were reacting a year to a year and a half ago when people were videographing them. They were attacking them, taking their phones, locking them up," said Jose LaSalle of the Cop Watch Patrol Unit.

The officer has had his gun and badge taken away as internal affairs investigates the case.

Police say the car that was initially stopped was stolen from Connecticut. They say it had 25 rounds of ammunition and some marijuana in it.