Rob Gronkowski -- HITS KATY PERRY CONCERT ... After JLo, Beyonce Shows

Rob Gronkowski's obsession with "she-pop" concerts continues ... now, the New England Patriots tight end hit up a Katy Perry concert n Connecticut ... and TMZ Sports has the footage.

A mohawk-sportin Gronk stood head and shoulders above the crowd at the Mohegan Sun show on July 7th -- the 3rd in a series of pop shows Rob has attended recently.

Back in June, Gronk rocked out at a Jennifer Lopez show ... and last week, he let loose at a Beyonce concert in Massachusetts.

Only difference between those shows and Katy Perry -- so far, we haven't seen any footage of Gronk dancing his face off ... like he did for Bey and JLo.