'TMZ Hollywood Sports' -- Blake Griffin Slap-Gate ... Star Witness Emerges

Did Blake Griffin slap a man across the face in a Vegas nightclub? We're talkin' to a big celebrity (like 7-foot tall) who was THERE when the alleged incident went down.

Make sure to check out the brand NEW episode of "TMZ Hollywood Sports" on Reelz -- every weekday at 8pm ET, 5pm PT.