Gronk Scores Cameo In Katy Perry Video, Ditto for Karl-Anthony Towns

Katy Perry just hired a bunch of HUGE athletes for her new music video -- everyone from Rob Gronkowski to Karl-Anthony Towns ... even Joey Chestnut!!!

It's all for Katy's new "Swish Swish" video -- which all takes place at a basketball game, with Bill Walton and Rich Eisen announcing.

Some of the highlights ... Katy "Kobe" Perry takes on the guy who plays The Mountain on "Game of Thrones" while Chestnut slams down hot dogs in the crowd.

Gronk holds a sign. Karl-Anthony busts out the "Backpack Kid" dance.

Good times.