The G.O.A.T. decided to give defense a try when he hit up a Fanatics charity event in Miami on Tuesday ... and TB12 put the clamps on a young girl who dared test the 7x Super Bowl champion!!

Check out the clip -- the newly retired signal-caller might've missed his calling. The young wide receiver tried to shake Brady with a 5-yard hitch, but he wasn't fooled, reaching in his arm to break up the pass.

Then it was tip drill time ... the ball floated in the air, Tom intercepted it, and took it to the house, shaking a would-be tackler with a move that would make Barry Sanders blush (not really).

The whole Fanatics shindig, called "Merch Madness," was pretty amazing -- more than $20 million in sports apparel was handed out to underserved families throughout the country as part of the organization's Merch Madness: Fan Gear Giveaway.

Cities like L.A., Philly, Miami, and New York all hosted events ... with Brady, DJ Khaled, and Odell Beckham Jr. all making appearances at the Carver Ranches Boys & Girls Club for the Florida location's festivities.

The event will take place every year.