Steven Purugganan, a spindly 8-year-old, was aimlessly clicking the TV remote when he caught sight of the sport that was to make him a world champion.

On television, children his age were stacking plastic cups into pyramids, then taking them apart as fast as they could. An excited crowd whooped and an announcer breathlessly reported their finish times.

Steven was intrigued. He wondered what it would feel like to have hundreds of fans. So his mother bought him a set of cups. "Now I know," he says three years later.

Steven, today a slight 11-year-old, was mobbed like a rock star as he strode through the World Sport Stacking Championships earlier this month at the Denver Coliseum in his blue Team USA shirt. Squealing girls pressed close to have their pictures taken with him; little kids asked for autographs; a film crew from Singapore cornered him for interviews.

Once a gym-class curiosity, cup-stacking has grown into an international craze, with Steven - a shy sixth-grader from Longmeadow, Mass. - its unlikely star.

"Some people call me the Tiger Woods of sport stacking," he says, his voice betraying a touch of awe at the comparison.

Nearly 700 athletes from a dozen countries - including Colombia, New Zealand, Switzerland and Taiwan - traveled to Denver for the tournament. The arena echoed with the click-click-clicking of plastic cups rising and falling at blazing speeds. Referees in striped jerseys huddled around video cameras, studying replays frame by frame to look for disqualifying moves, such as touching two stacks of cups at the same time.

British coach Ron Parker paced restlessly, his back to his athletes. "I can't watch them," he said. "It's the nerves."

Sport stackers work with a dozen 10-ounce plastic cups that look as if they could hold Slurpees, except for the holes punched in the bottom to prevent suction. The athletes start with cups divided into three stacks. Then, in a series of choreographed motions almost too quick for the eye to follow, they grab several cups with each hand and drop them one by one into precise pyramid patterns. They finish by collapsing the cups back into stacks.

Stackers compete in individual time trials, relays and in doubles races that require partners to hug each other around the waist so each uses just one hand.

The origins of cup-stacking are murky. But a suburban Denver teacher named Bob Fox is widely credited with turning it into an international obsession.

Fox, now 51, fell in love with stacking - "upside-down juggling," he called it - when he saw a troop of children showing their skill on "The Tonight Show Starring Johnny Carson" in 1990. When he began teaching physical education five years later, Mr. Fox introduced stacking to his classes as a "circus art," alongside unicycling.

"My kids just went nuts," he says.

Then Hasbro Inc., the company making the cups, discontinued the line. So in 1998, Mr. Fox and his wife, Jill, decided to create their own brand of cups and introduce the sport to P.E. teachers nationwide. A decade later, their business has representatives promoting the sport in 22 countries and rings up $4 million a year in sales, according to Mr. Fox.

"We're the first to admit stacking cups sounds silly," Mr. Fox says. "But in 1891 when James Naismith came up with the idea of throwing a soccer ball into a peach basket nailed to the side of a barn, it sounded pretty silly, too."

Sport stacking is oddly fascinating to watch; the best videos on YouTube draw more than 500,000 hits.

Fox touts the benefits for participants: The repetitive motion improves hand-eye coordination and reaction time, according to a study published in the journal Perceptual and Motor Skills. All ages and fitness levels can compete at stacking, from preschoolers to senior citizens. There's even a tournament division for disabled competitors.

Also, it is - at least, so far - a scandal-free sport. True, a few children wash their cups in soapy water to make it easier to slide them from a stack. But that's about it.

"I haven't heard of any steroid use," Fox says.

Indeed, Luree Copeland, a 63-year-old stacker from Nebraska, recoils at the suggestion that she consider arthritis medication to loosen her stiff hands before competition. Her preferred approach: "Take a deep breath and get focused."

Fox's company, Speed Stacks Inc., sells the only officially sanctioned tournament cups, as well as weighted training cups, dexterity-building minicups, slick stacking mats, precision timers and special backpacks to hold everything. It's possible to spend a small fortune on gear. But the basic setup is cheap: a dozen plastic cups and a stopwatch.

That makes it an ideal sport in the developing world, says Aristotle Alipon, the coach of the Philippines team. "It's perfect. Even tables are optional."

Many competitors believe cup-stacking should be recognized as an Olympic sport. It takes intense focus and a deft ambidexterity honed by hours of practice. Friends may scoff - "They think it's totally goofy," 17-year-old Dustin Gonzalez said at the competition - but veteran stackers know the truth: Fingers cramp. Legs tremble. Foreheads bead with sweat.

Joel Brown, 14, looked down at his arms in wonder after helping set a world record in a relay. "I'm shaking!" he said.

To condition his team, German coach Burkhard Reuhl draws on drills he learned from decades in track and field, though he keeps the details secret. All he's willing to say is, "We train quite seriously."

Purugganan devised his own training program by watching top stackers on video and was soon clocking world-record times, such as a blistering 1.80 seconds to build and collapse a trio of three-cup pyramids. Steven's face tenses in ferocious concentration when he stacks, but his touch on the cups is light and smooth.

At 56 inches, he's the perfect height for regulation stacking tables, which are 29 to 31 inches tall. Bigger children must take an uncomfortably wide stance, almost as if they're doing splits, to keep their hands level with the cups.

But Steven says the secret of his success is simply practice - often three hours a day. "We're amazed at how he manages to focus," says his mother, Vicki Purugganan.

That focus was evident as the championship swung into final-round action on a red-carpeted stage, under banks of bright lights. Hundreds of spectators shouted and waved flags. TV crews bustled about.

To groans from the crowd, several top contenders fumbled, tipping over cups. That isn't a disqualifying error, but it is a fatal one in a sport in which races are won or lost by hundredths of a second.

Then Steven stepped up, and in a 2.15-second blur, assembled and knocked down two three-cup pyramids and a six-cup stack. There was a nervous hush while referees reviewed the video. At last, they held up a green card: No infractions. "A new world record!" the announcer shouted.

Trotting offstage, Steven grinned. "I feel really great," he said. "That's really fast." Then he handed his trophy to a coach and scrambled over to the practice table. He had cups to stack.