[YouTube video link, the incident occurs at 1:40.]

Above, a video that shows a white-shirted NYPD officer punching a person in a green shirt, around one minute 40 seconds in. The person is Felix Rivera-Pitre, reports Gothamist. He tells Gothamist that he is HIV positive and is a former dancer:

[Rivera-Pitre] tells us he was walking a little bit in front of the police on William Street, and admits he "shot the cop a look." But then, according to Rivera-Pitre (and this is in line with what we witnessed), "The cop just lunged at me full throttle and hit me on the left side of my face. It tore my earring out. I remember seeing my earring on the ground next to me and it was full of blood. I was completely dumbstruck. I'm HIV positive and that cop should get tested."

More at The Street and at Animal New York.

Mr. Rivera-Pitre later told reporters that the officer who punched him should get tested for HIV, because the punch drew blood. I am not an expert on HIV transmission, but do not believe this to be an accurate risk scenario—perhaps others more familiar would like to weigh in, in the comments.