Sorry, Tom Brady ... Rob Gronkowski looks like he's OFFICIALLY moved on from football -- and onto acting -- 'cause the retired Pats star killed it as a fake cop at the Billboard Music Awards!!
It all went down Wednesday night ... when Gronk kicked off the BBMA show as a "security guard" who was bouncing Kelly Clarkson.
The skit was pretty funny ... Gronk pretended to kick K.C. -- who he called a "seat filler" -- out of her spot to let Florida Georgia Line take her place.
Looks like @RobGronkowski learned a few things from @goon356.