This weekend, they will come from every corner of the country to explore every nook and cranny of Sin City. They should feel quite at home there. After all, they are people who willingly associate themselves with names like Ballz Deep, Gone Nuckin' Futz, Multiple Scoregasms, Stewies Sexy Party, Tricky Bunnies, The Royal Tennenballs, Galactic Prophylactic, We Kick Your Balls and, of course, Valley GIRLS GIRLS GIRLS.

So, you say, these visitors must be participants in the Adult Entertainment Expo.

Nope. Those are team names. Kickball team names.

Yes, kickball. The sport you played in physical education class, or at recess, when you were six. The sport that required little more than a rubber red ball, four makeshift bases and thick enough skin to endure a little sting.

That sport is now a full-fledged co-ed adult fad, being played in organized contests by twentysomethings and thirtysomethings nationwide.

In fact, the World Adult Kickball Association (WAKA) has a full-time staff of 25, necessary to accommodate the exploding demand. WAKA sponsors more than 300 divisions in 33 states, plus Washington D.C., and claims more than 25,000 registered players, most paying roughly $60 to $80 for a season.

WAKA invites 72 teams from 18 states to its annual national tournament, this weekend's called Founders Cup XII. That's 24 more teams than it invited to Las Vegas in 2008, 53 more than it invited to Boston in 2007 and 56 more than it invited to Miami in 2006.

That means a lot of booked rooms at The Platinum Hotel & Spa, a lot of used fields at Desert Breeze Park, and a lot of chugged beers under a tent by spectators and participants alike.

"The generational divide that says you can't like something after a certain age ... that has broken down," Christopher Noxon, the author of Rejuvenile: Kickball, Cartoons, Cupcakes and the Reinvention of the American Grownup, said after rolling out the ceremonial first ball in Miami three years ago. "While it's easy to be cynical about it, it rises out of a very human impulse, a genuine place. Plus, kickball's just a hell of a lot of fun."

Nathan Wauk / WAKA Arone from the Rhino Stampede throws a strike during a North Hollywood playoff game.

And it's quite a success story, considering that it started as brainstorming between buddies over beers in a Washington D.C. bar. Back in 1998, during the dot.com boom, computer guys Jimmy Walicek, Johnny LeHane and a few others were seeking a new way to socialize. They decided to start something for locals who wanted to relive their childhoods and make a few friends.

"It was really fun," says LeHane, now 37. "So we decided to figure out how to register people and get people out. The internet was a quick way to do that."

A whim became a career. Some traditions and many rules took root. Each team had to field 11 players at a time, and at least four players of each gender, all at least 21. There were 60 feet between bases, no outs recorded for hitting baserunners above the neck, and a strike zone measuring one foot to either side of home plate and one foot high. Regional divisions were encouraged to find local bars to be sponsors and host postgame parties. And, for those with a knack for rolling, kicking, catching and throwing, the Founders Cup became the ultimate goal.

"At the local level, it's pretty much the same as it's always been," LeHane says. "People join to have a great time. You get to be silly with a big red ball. But, where it counts, at Founders Cup, it continues to get more and more competitive."

WAKA Kickball players enjoy some adult beverages in Miami.

It's so competitive that the officials are required to pass a written test, and must receive recommendations. It's so competitive that, to make the game harder for pitchers, they must make the ball bounce at least twice before it reaches the plate. It's so competitive that some players even delay their drinking until after playing the nine games in one day that could make them champions.

And, for these guys and girls, that self-control is quite an accomplishment.

After all, the Founders Day Weekend ends with what WAKA touts at the World's Largest Flip Cup tournament, which essentially involves swigging as fast as you can.

And, after all, these are some of the other team names:

Party Foul. Happy Hour. And yes, Menace to Sobriety.

All of those teams will be taking direct aim at LaSalle Blanks' Frosty Balls.

"We are going back to Vegas to give it our all," Blanks boasts. "If it is in the cards, no pun intended, then we will gladly bring that trophy back to Hampton Roads. It will take a monumental effort to beat us."