I can't tell them to get off my lawn

I don't have a lawn. They were on the high school's lawn, across the street (not to mention a block away and 6 stories down.) The cheerleaders started a little before 8am. I said something very rude. Redbird was right beside me, but the cheerleading was loud enough that she had trouble hearing me. She thought they were chanting, "Let's Go, Waltham!" and suggested they take themselves right back to Waltham. As the cheerleaders became more practiced at chanting in unison (though not louder--they were loud from the start), it became clear that their refrain was, "Let's Go, Walkers!" with variations about walking. Although she and I usually walk quite a bit, the noise inspired us to consider a drive to spend the day out of earshot. We put on loud music, with the cheerleading coming through strongly between songs (sometimes between bars.)

It stopped at 10:30am. I have no idea what the racket was about. There's no mention of it in the online version of the local newspaper. In retrospect, the signs near the high school are clearly related to the event...but they are just big white arrows on black posterboard, pointing in the direction of the school. When I saw them yesterday, I didn't know who had put them up, or why. They're organized enough to have cheerleaders, lots of portable toilets, and matching green t-shirts (The high school teams wear maroon.) Who were those masked cheerleaders?