Taking dirt bikes from the back roads to the big-time arenas, supercross is the fastest-growing motor sport in the world, quickly catching up with NASCAR in popularity. Last year's Phoenix event attracted more than 49,000 fans -- a Bank One Ballpark attendance figure topped only by the World Series.

In nearly every city hosting one of these races, "it's outselling their own NFL team in their own stadium," says Mark Abernethy, spokesman for Clear Channel Entertainment's Motor Sports division.

Growing legions of fans for this extreme sport are drawn not only to the raw energy of the races, but to the bold athleticism of the riders, who use their whole bodies to handle the bikes. Catching air and handling the sharp curves requires incredible strength and agility.

Watching the competition is very emotional, too, says Honda Racing Team member Ernesto Fonseca, 125cc Western Regional Champion for 2001. Having trained since the age of 5 in his native Costa Rica, Fonseca was 11 when he finally visited the U.S. to compete.

"The first time I ever went to a supercross, it really gave me chills because I knew how hard it was," he says.

Fonseca especially encourages curious first-timers to check out the action. "You'll be amazed," he promises.