In the ground video the first time the ground controller said "knock it off" it sounded like he said it over the PA system to the fans and then said it over the radio to the aircraft. I'm no expert over thunderbirds procedures but i am pretty sure the announcers voice along with radio communications are recorded thats why he said "knock it off" twice. If you notice immediately after the second "knock it off" the planes started responding immediately. Thank god the pilot made it out ok and no one on the ground was injured.