Rockridge BART users, beware. If you're walking through the station's parking lot Thursday nights, you best prepare for a challenge. You may try to slink by, sapped by a long day at the office. But you'll be hard pressed to pass without a fight.

"It's one of our main recruiting strategies," said Sam Wong, 27, of Oakland. "A lot of people come through when they're walking to their cars. Everybody's looking. We're not afraid to call you out: 'Are you looking at us?' For the most part it works.

"We're pretty nice," he continued. "We're not going to jump you. We just want to play games."

Wong's game of choice is four square. You may remember it, albeit hazily, from grade school. Four players, four squares in a, in this case, 20-by-20 grid. Extra players wait in a line nearby. After the serve, players must knock the ball, without catching it, into another person's square. The first player to fail is sent to the back of the line, which opens up one box. The remaining players shift counterclockwise to close any gaps. And the first person in line moves into the bottom, lower left, square. Repeat as desired.

Wong and some friends put together the weekly game in June 2008. The cash outlay was low: sidewalk chalk at 99 cents and 6 bucks for a ball that lasts 6 months. And, without much ado, 4 Square of the East Bay was born.

"It is a competitive game. It is a game where people can get hyped up. But it's not an event where you're going to get belligerent," Wong said. "There's something about playing a kid's game at an adult level. It's a little bit of a throwback. A little bit whimsical. It's not as serious as football and baseball. And there's room for freedom and originality."

Players bring their own styles to the game. For Wong, it's a martial arts approach. Others are silly or haphazard. Just about anything goes.

"I do crazy spins and jump hits, but that doesn't mean that's going to work for you," he said. "Maybe you're more of a soft touch player, you fake people out, distract people to your advantage. You'll identify what works for you. It's about being able to be okay with your own personal style. If you're willing to act a little foolish, you're going to have a better time."

Originality also enters the game via special rules created by the player in the top left square, "A" square. Rules can run the gamut. Use just the left hand or hop on one foot throughout the round. Make a sound like Prince singing before the bounce. Or there's the "one word story" rule – each person adds a word, making a story with the prior contributions, before striking the ball. Then there's the ever popular pirate rule: Keep one eye closed throughout the round.

"That takes away your depth perception," Wong said. "It detracts from the physical action. It's not just about hitting the ball hard and fast and doing crazy moves. It's about integrating a thought process behind it."

Wong had heard about other groups – Oakland bike polo enthusiasts and members of the Society for Creative Anachronism (who reenact medieval history) – that use the Rockridge BART parking lot Thursday nights.

"We just thought we'd go hang out near bike polo and the people with the swords and try to bring out more people. It was a chance to be part of this kooky retaking of public space," Wong said.

Wong, who is from the Bay Area, started playing four square as a student at Bard College in New York. Initially he was part of a ragtag breakdance crew that met weekly.

"We would always breakdance on Wednesday nights in one of the common spaces," he said. "We would try to get other people to come through and break with us. And people were like, 'We'd love to, but we have to go play four square.' We were like f-ck four square!"

Then he started dating a four square girl and his Wednesday nights were never the same. The Bard players were "maniacs," bouncing off the walls and diving, doing crazy spins and playing mind games. There were DJ battles every week, with kids going head to head with the tracks on their iPods.

Wong returned to Oakland in 2005 after graduating, and decided last year to bring the game to Rockridge. Oakland has a rich tradition of urban games, capture the flag at City Hall being one prime example. Adult four square clubs dot the United States, and are particularly active in Boston and Brooklyn.

Local ballers have ranged in age from 8 to 62. In a normal week, about 15 people join the game, but the number has swelled at times to closer to 45.

It can get rough. But Oakland resident Jordan Blanks, who broke her foot during a game earlier this year, said four square is a great way to relieve stress. Blanks attends nursing school and works as a childcare provider.

"Part of it is the excitement of hanging out with other people who would find childhood-activities-as-grownups fun, finding likeminded people. It's also about being able to act like a kid again," Blanks, 25, said.  "I come really bogged down, not feeling good, and by the time I'm leaving, I've laughed at least three times."

In March, Blanks jumped up to hit the ball and landed on her pinky toe, breaking her metatarsal bone in several places. After surgery, she tried to play on crutches but fell "on my butt." She took several months off, but returned to the game as soon as she could, in early July.
 
"Especially in Oakland, people can kind of be in their own boxes and not really talk to each other," she said. "It's an opportunity to build community toward a common goal of just having fun and talking to people we might not normally get to know."

Organizer Wong said the game is, well, more than a game.

"Even if four square isn't your thing, what it symbolizes is that you don't need to have a lot of resources to have a good time or enjoy people. Four square is not material based, it's relationship based," he said. "And that's something people forget sometimes, or choose to forget. Even if we're not your cup of tea, you can still do your own thing and there will be a group of people out there who will support you."

Games happen every Thursday at 9 p.m. in the Rockridge BART parking lot. For more information, visit http://myspace.com/4squareeastbay. Find 4SEB on Facebook. And watch more videos here and here.