UFC Fighter Derek Brunson -- Don't Mess With Me ... I'll Cheer Your Ass Off! [Video]

WE'VE GOT SPIRIT, YES WE DO! WE'VE GOT SPIRIT, HOW 'BOUT YOU???

That's right, before UFC fighter Derek Brunson was a face-smashing bad ass ... he was a sweater-wearing, spirit-filled, HIGH SCHOOL CHEERLEADER with amazing moves ... caught on video.

Brunson -- who dominated in Strikeforce and is now making his Octagon debut in UFC 155 -- tells TMZ ... he ditched the "sport" after snagging a wrestling scholarship at UNC Pembroke.

As for his upcoming bout tonight, Brunson says ... "I'm getting my hand raised. GO BIG OR GO HOME."

Which kinda sounds like something a cheerleader would say ...