Suge Knight punched a guy hard at an L.A. pot dispensary ... and we got the surveillance video.
TMZ broke the story ... Suge got angry at an employee ... allegedly threatening to kill the guy .... after the rapper was told to leave because he didn't have a medical marijuana card.
When you watch the video, things start out friendly enough inside the pot shop -- called Medstar Collective -- but turn ugly quickly. Suge and the employee walk out and the mogul socks the guy in the jaw without warning ... then storms away.
The employee filed a police report and the cops have the video. Suge is being investigated for making felony criminal threats.
Suge's position -- he agreed to make an appearance for cash and weed and they went back on the deal.