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Another ferocious assault involving a Baltimore superstar ... the Orioles mascot ... who got HIT IN THE BALLS by a dumbass fan AND FOUGHT BACK ... and TMZ Sports has the footage.

Our MLB sources tell us ... the incident went down at Oriole Park at Camden Yard in April 2013 when a seemingly drunken O's fan approached the mascot for a photo -- and then suckerpunched the bird right in his feathered crotch.

The bird executed a perfect judo-style legsweep ... and took down the attacker.

Our sources tell us ... the nut-puncher was arrested moments after the camera shut off.