Zac Brown -- 'MIDGET BOWLING' in South Dakota

Country superstar Zac Brown felt like doing a little bowling this weekend ... so he greased up a little person and BOWLED him at some pins ... and it was all caught on tape!!!

It all went down at the the Sturgis Motorcycle Rally in South Dakota ... where Zac was enjoying the "Midget Bowling" tournament at the M F'N Bowling tent.

For the record, events involving the tossing or throwing of little people is generally frowned upon by the little person community ... but event organizers insist "Midget Bowling" is perfectly legit.

In fact, TMZ spoke with "Short Sleeve Sampson" -- the self-described "midget" at the center of the action -- who tells us he was a ready and willing participant in the activity ... and insists Zac didn't do ANYTHING wrong.

Sampson claims "midget bowling" is safer than "midget tossing" because the little people are never airborne ... "it's just a modified slip and slide."

As for Zac, Sampson says he's PROUD of the "Chicken Fried" singer ... 'cause he hit a strike on his very first roll.