It's the Frisbee of the '80s," says one devotee, and time may prove him right. It costs only $8, and considering the fact that they are selling at a rate of nearly 100,000 a month and two million have already been sold, the small, pellet-filled bag called Hacky Sack is beginning to make Trivial Pursuit seem, well, trivial. "It's addictive," says John Stalberger, the businessman credited with developing the sport. "There are no winners or losers. Kids who have a hard time with aggressive team sports find they're great at footbag."

The object of the game is to keep the footbag aloft as long as possible, passing it from foot to foot using knees, head, virtually any part of the body except the hands or arms. Part of Hacky Sack's appeal is that it can be played alone (the world solo record holder kicked the sack 17,872 times), in groups or with competitive teams.

Footbagging is not exactly an original idea. Similar games were played in the Far East centuries ago. Stalberger "discovered" it in 1972 when, as a college student at the University of Texas, he suffered a knee injury playing football. Despite a cartilage operation and rehabilitation programs, his knee remained stiff.

On a trip to Portland, Oreg. Stalberger met handyman Mike Marshall, who taught him a "funny" game he played with a beanbag and, says Stalberger, "It turned out to be exactly what I needed. It actually created a cross section of flexibility through the knee region." They developed the two-man game and were soon inviting each other to "hack the sack."

Then in 1975 Marshall died of a heart attack at 28. Stalberger's devotion to the game and to his friend convinced him that he should pursue the project. After persuading a few local sporting goods stores to stock some Hacky Sacks, he talked high school athletic instructors into letting him demonstrate the game in their classes. "The kids got hooked. They wanted to know where to buy these things."

Last year he sold his patent to Wham-O Inc. (manufacturers of the Hula Hoop and Frisbee) for a six-figure fee. Stalburger is now a consultant for Wham-O and travels worldwide demonstrating Hacky Sack. He predicts that Hacky Sack will someday make it as an Olympic event. For Stalberger, that would be the biggest kick of all.