Donnell Rawlings allegedly popped a dude in the face ... and now cops are on the case.
Law enforcement sources tell TMZ ... 20-year-old Thurston Greer claims at 2:30 AM Friday Rawlings socked him in the noggin with a closed fist outside a NYC hotel, resulting in pain, swelling and scratches on his arms.
Greer tells us he ran into Dave Chappelle walking out of the hotel bathroom and asked for a pic ... but Dave declined. Greer claims he then went outside the hotel and began recording a Facebook Live video to tell friends what had just gone down. He says Donnell, Chappelle and a security guard walked out of the hotel, saw him and got angry, thinking he was persisting to get a photo.
Greer says he scuffled with Rawlings and security after they tried taking his phone, and that's when he got punched.
Chappelle's not listed in the police report, but cops want to talk to Donnell. Greer tells us he's already met with an attorney and is considering legal options.
A source connected to Donnell says Greer was extremely intrusive, trying to take pics of them while they were in the bathroom. The source says Donnell never punched the guy ... he took a swing, missed and fell to the ground. The source adds Greer was "aggressive" and determined to get photos to post on social media.