William Orrell is the best in the world in his sport. A 17-year-old from North Carolina, Orrell is ranked No. 1 and is the reigning junior Olympic and world champion. He has a popular YouTube channel, a product line named after him, and legions of admiring fans in dozens of countries.

He has gained all this notoriety by stacking cups in small pyramids at a mind-boggling clip.

“A lot of people don’t think it is a sport,” said Orrell, who will defend his world title at the World Sport Stacking Championships, which begin Saturday in Speichersdorf, Germany. “But why is stacking cups any less important than putting a ball in a hole or through a hoop?”

A casual game that started with Dixie cups at a Boys & Girls Club in Oceanside, Calif., more than 30 years ago is evolving into a fast-growing sport that is part of the physical education curriculum at thousands of American schools. More than two dozen nations will field teams at the world championships, and stacking is growing fastest in Asia, where children as young as 10, like fifth-ranked Chan Keng Ian, are helping to globalize the sport.

Stacking has been an A.A.U. Junior Olympics event since 2012, alongside swimming, karate, and track and field but also baton twirling and jump rope. School districts like stacking because it is low liability and anyone can play, even children with physical or mental disabilities.