Police Investigating Vid of Lil Scrappy Stage-Crasher Falling on Head

Lil Scrappy's recent performance in Columbus, OH hit a snag when a man rushed the stage, only to get knuckled before he bucked -- and police are now investigating the case!!!

Sgt. James Fuqua of the Columbus Police Department tells TMZ Hip Hop that police weren't originally notified of the head-bussin' incident ... but investigators say they are now combing through the video.

Scrappy was performing during the Day 2 lineup for the SUMMER614 — Where Music is Therapy Festival, when a man crept up from the side of the stage and climbed onto a speaker -- only to be pushed with tremendous force by another man standing onstage before he could even make it on the platform.

The stage-crasher appeared to backflop on the pavement, where he stayed motionless for the duration of the video.

Scrappy even stopped performing after realizing the guy wasn't moving!!!

Social media users who claimed to have been at the event say the man was leaking blood from his head as he lay on the ground unconscious for several minutes.

It's unclear whether or not the onstage roadblock was a member of Scrappy's security squad, but Sgt. Fuqua tells us if the victim has not filed a complaint, then there will be no charges.