CAMBRIDGE, Mass. — The Cambridge police have launched an internal investigation into an incident on Friday night in which officers tackled and punched a black Harvard student they were trying to arrest as he stood naked in the median of a busy street.

The police, who released a video of the scene on Sunday amid complaints about the officers’ conduct, said that the student, Selorm Ohene, 21, was apparently high on drugs and acting in an aggressive and unruly manner when they approached him and tried to calm him down. He came at them, the police said, with clenched fists.

The video of the incident shows a few police officers standing in a circle around Mr. Ohene for several moments. As he stepped toward one officer, a second officer dove at his legs from behind, the video shows, and Mr. Ohene and the officers fell to the ground. Mr. Ohene could be heard crying out at that point. At least one officer then could be seen punching Mr. Ohene, and the police have acknowledged that an officer punched him five times in the stomach.

The Harvard Black Law Students Association, some of whose members witnessed the scene, disputed the police account and said the officers acted without provocation.