Kentucky QB -- KNOCKED THE HELL OUT ... By Rival Football Player [Video]

University of Kentucky QB Drew Barker was SOCKED HARD and knocked to the ground ... in a brutal sucker punch attack in the lobby of a university dorm ... and the attacker was a former UK player.

It all went down on the campus of Eastern Kentucky University on January 25th -- after 3 UK players got into a bar fight with a member of the EKU football team earlier that night.

19-year-old Barker and some of his teammates went over to the EKU dorm -- where EKU lineman Patrick Graffree entered the dorm, took off his shirt ... and clocked Barker in the side of the head.

FYI -- 21-year-old Graffree (6'4", 295 lbs) played for UK before transferring over to EKU.

Police investigated the incident ... but shockingly, no one was prosecuted.