IF YOU FREQUENT the Mall on weekends, the odds are probably good that you've run across the D.C. All-Stars. They're the ones set up two or three Saturdays each month near the Smithsonian Metro, kicking a tiny multi-paneled bag across a net in a constant series of whirls, dives and leaps. You may have even been one of many to comment, "Hey -- it's Hacky Sack volleyball!"

Well, no, but close enough. And the members of the self-titled All-Stars, the metro area's only activefootbag club, won't hold it against you. After all, how were you to know that the game is called, with perfect economy, "net"? And that what you might remember as a school days fad is now a growing participatory sport, combining elements of X-Games' swashbuckling, performance art flair and martial arts concentration?

First, the name. Though there's nothing wrong with that other term, footbag has become the word of choice. The popular conception of Hacky Sack, after all, is of a fairly frivolous activity. The setting is usually a high-school hallway or college campus, or perhaps a Phish concert. The scene: overly relaxed circles of slackers pay half-attention to a psychedelically striped bag that seems to spend most of its time being retrieved from the ground after missed kicks.

This laid-back, communal "hacking" still proudly exists, but footbag has, in the meantime, become very much its own sport, and a physically demanding one at that. Footbag net is played in singles or in pairs on surfaces the size of a badminton court and utilizes the scoring rules of volleyball. Games are punctuated with ferocious spikes and "jousts," foot-to-foot meetings over the net that call to mind Jackie Chan far more than Jerry Garcia.

Freestyle footbag, on the other hand, is a more direct descendant of the familiar "hack circle." Freestylers, alone or in groups, try to tie together fundamental tricks such as "toe-stalls" (stopping the bag on the top of the foot) and "clippers" (catching the bag on one foot crossed behind the other) into complex packages with wonderfully evocative names: "rip-walks," "blurry eggbeaters" or the never-before accomplished, six-element "Nemesis." To watch a good freestyler in a groove can be mesmerizing -- in the best routines, the bag seems to hover magically in place as the player engages in a frenzy of hopping and twisting.

Though it might seem a sport for spur-of-the-moment temperaments, footbag offers plenty of structured opportunities for aficionados to meet, greet and compete. Two weekends ago, for example, the D.C. All-Stars were in Chicago for the World Footbag Championships, where they competed against nearly 200 other kickers from all over North America for just enough individual prize money -- between $50 and $150 for high finishers -- to justify some use of the word "professional."

Not that your average kicker makes any kind of living at it. Club members pay their own way to tournaments and usually crash with friends or hotels offering special tournament rates. The D.C. All-Stars aim to attend about four events each year, ranging from a regular East Coast championship every spring in Harrisburg, Pa., to sites as far away as Palo Alto, Calif..

Every grass-roots sport must have its gurus and legends, and when it comes to D.C.-area footbag, all roads seem to lead through Vince Bradley, 28, a self-described "fogy," which in this context seems to mean anyone approaching the age of 30. Neil Payne, who works days for a nonprofit educational organization, credits his avocation as a freestyler to a random meeting with Bradley on the last day of 1995. Driving along 18th Street in Adams-Morgan, Payne happened to see Bradley and Jane Jones, a top female footbagger now based on the West Coast, standing on the sidewalk and seamlessly stringing together one move after another, oblivious to pedestrian traffic.

"I'd been in lots of hack circles where you'd learn one trick and then that was it, people would cheer and you'd move on to another one," Payne says. "But seeing them link together all these tricks, I had no idea it was even possible." Payne joined the two that day, learned a few new moves, and here Bradley can pick up the story: "I dragged him over to my car, gave him an I Dig 14-panel footbag, and that was the beginning for Neil."

Jeff Bowling, an employee of the University of Maryland, also has Bradley, a computer programmer at Maryland, to thank for his introduction to the sport. Several years ago, Bowling, then a high-school soccer player, bought a footbag to hone his eye-foot coordination. He played with it for a few days, and then promptly lost it, as he puts it, "probably on the roof of my house somewhere." A familiar story, surely. But years later, as a student at Charles County Community College, Bowling was killing time between classes when he happened to see a demonstration run by Bradley and was "blown away."

"At first I was just intimidated," Bowling says. "They were playing net, doing all these jousts and leg-whip stuff, and I thought there was no way I could ever even approach them. But Vince called us over, told us he'd help us learn and took time to answer all of our questions."

Bowling and the other D.C. All-Stars understand only too well that images of high-flying (and hamstring-endangering) net action might frighten off potential players, and so they're eager to point out that kickers of every ability level are welcome, just as Bradley once welcomed them. At least in this fashion, serious footbag remains true to its more casual, hack circle roots. If you see the All-Stars there on the Mall, they say, don't be shy; if you're willing to learn, they're willing to teach.

For perfect proof of footbag's populist philosophy, look no further than Matt Quint, an employee of the Australian Embassy. It took nothing more than a chance encounter after a day in the Smithsonian museums to make Quint a member of the club. "I woke up from a nap on the Mall and there they were," he says. "I decided to walk over and see what was going on."

Four years later, he hasn't stopped kicking. "I'm still here," Quint adds, and he laughs. "So I must have liked what I saw."

D.C. ALL-STARS -- For information, contact Jeff Bowling at 301/990-0339. Mail-order merchandise and tournament schedules can be found on a comprehensive Web site: www.footbag.org. The World Footbag Association in Colorado also sells merchandise: 800/878-8797. Web site: worldfootbag.com.