On the afternoon of March 28, Kyle Gadke was busy with a private cheerleading lesson. When his student took a water break, the 26-year-old, Illinois-based coach looked at his phone and saw an email ...

One after another, a dozen young cheerleaders raced across a springy blue mat and flung themselves into a series of roundoffs and backflips, the thump of their hands and feet reverberating through the ...