On the first and third Sunday of every month, Mr. Ko, 34, a mechanical engineer from nearby Santa Clara, organizes Segway polo matches with friends and colleagues, most of whom work in the Silicon Valley, all of whom belong to the Bay Area Segway Enthusiasts Group.

Their matches have some of the trappings of traditional polo. Players wear jerseys – actually, colored T-shirts – and use mallets to knock a ball into a goal. Score is kept. And there is an umpire, although players feel free to ignore his calls.

“There are a few guys who take it seriously, but mostly this is a big goof,” said Jon Bauer, 37, of San Francisco.

This morning’s contest pitted four against four. Mr. Bauer’s team wore blue T-shirts. Mr. Ko’s team wore yellow and included Stephen G. Wozniak, one of the founders of Apple Computer and the owner of seven Segways. He is respected, if not feared, on the polo field for his aggressive play.

“My swing feels off,” Mr. Wozniak said just before the match began. He whirled his right arm in a windmill motion and said that he was operating on virtually no sleep, having stayed up at a party and then to watch a movie until 8:30 that morning.

The teams lined up on opposite sides of the field and rushed toward each other when the umpire rolled the ball between them.

At first glance, Segways could be mistaken for large push mowers, and in the early going, as the players found their rhythm on the grass, the game resembled a frenzied act of landscaping. But near the end of the first period, or chukker, in polo parlance, both teams showed signs of organization, even fleeting hints of skill.

“You should have seen us at some of the first games,” Mr. Bauer said. “We were all bunched together. Not much passing. Very little strategy.”

Like the birth of polo, placed variously in Persia or India more than 2,000 years ago, the genesis of Segway polo is hard to pin down. Mr. Ko traces his own interest in it to the fall of 2003, when a Segway polo demonstration was staged during halftime of a professional football game.

“I didn’t see it,” Mr. Ko said of the halftime show. “But it sounded pretty cool.”

Jonathan van Clute, a real estate and stock investor from Sunnyvale, said he had stumbled onto the idea even earlier, while consulting at a software company. “I brought my Segway into the office so everyone could goof around with it,” he said. “And this one guy pokes his head through the door and says, ‘Dude, two words: Segway polo.’ ”

WHATEVER the case, in April of last year, Mr. Ko and Mr. van Clute met at Ponderosa Park and began to tinker with their version of the game. Mr. Ko fashioned a mallet out of plastic pipe. They tried different types of balls before settling on a Nerf. They adopted rules from polo, water polo and bicycle polo, another contemporary offshoot. They outlawed high-sticking, or the polo equivalent of it, and agreed to run their Segways on the yellow-key setting – one of three settings on a Segway – limiting the top speed to eight miles an hour.

“We’ve never had any serious accidents,” Mr. Bauer said. “But there have been some pretty spectacular falls.”

During the match, the prospect of injury seemed to heighten whenever Mr. Wozniak entered the fray. Despite sleep deprivation, he played with zeal, charging after loose balls, leaning forward on his Segway like a ski jumper searching for extra air.

Mr. Wozniak’s opponents attributed his fearless play to his competitive gusto and his fleet of backup Segways, not unlike a traditional polo player’s string of ponies.

“Woz is the only guy who’s always cranking his Segway at top speed,” Mr. Bauer said. “I think it has something to do with the fact that he’s the least concerned with damaging his.”

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