The game was tucked in the dark corner of the Cambridge Common last night, away from the lamp-lined paths and trees covered with Christmas lights. From afar, it looked like some kind of goofy science project: a pair of lights darting back and forth in the night. But when you approached the field and saw the players, you realized that it was something even more bizarre. Those floating lights were frisbees.

The Illuminated Frisbee Nighttime Throw-Around has been playing ultimate frisbee in the dark since June. Organized through Meetup.com by Chris Beaman -- a Joiner's joiner who has also started Meetups devoted to flag football, political documentaries, and Scrabble -- nighttime ultimate frisbee answered a practical question: How do you play ultimate in Cambridge when the Common's playing fields are always booked?

The answer, of course, was to play at night. Frisbees have an advantage over softballs and soccer balls: you can light them up with little more than an LED. Illuminated frisbees have been on the market for a while, but nobody in the Cambridge group had ever heard of a nighttime frisbee league. Not that something like that would keep them from starting one themselves.

"They make the disc, but I don't know of any groups with this level of organization, with the glowsticks and everything," said co-organizer Chris McClelland.

Each player wears a thin glowstick around the wrist. The devices allow players to find each other in the darkness and, because they come in different colors, make it possible to identify teammates at a distance. Last night, the colors were blue and something else. "Pink," said one player. "They are actually magenta," corrected another.

Arguments about hues aside, the game is played with a minimum of competition. "We play very loosely," said McClelland, addressing a group of newcomers. "We don't even keep score."

The organizers tweaked the rules of the game -- which involves advancing a frisbee toward a goal line one throw at a time -- to accommodate a variety of skill levels and to allow for the complications of playing in complete darkness. Out of bounds calls are never made, for instance, because it is impossible to see the boundary lines. Defenders, who in regular ultimate are allowed to guard players within a distance of one frisbee, must stand a minimum of three feet away from their opponents.

Courtesy is encouraged. Players are not allowed to heckle each other. Fouls are called freely. Hucking, or throwing Hail Mary frisbee passes downfield, is discouraged. "It's dangerous because if everybody is running full out, you'll run into people," explained frisbee regular Amy Spelz.

Despite all the precautions, though, accidents do happen, as Bostonist found out when we took the field. Reaching in the darkness for an errant pass, we ran cheekbone first into somebody's face. Moments later, regular player Amanda Maas fell directly into a puddle of mud. (She broke her fall and ended up with a pair of filthy forearms.) McClelland ended up with a fat lip.

When someone takes a spill, play stops. Other players literally trip over one another to lend assistance. Without a scoreboard, and the competitive pressures that it exerts, the players keep things positive.

"Everybody's so friendly," said Spelz, "and you don't have to be competitive, so nobody's going to scream at you if you miss a pass."

And the cordial environment doesn't end on the field. Though most players first hear about the game through Meetup, Maria Stack started playing when Beaman, her next-door neighbor, personally invited her. "That's community building right there," she said. "It's kind of rare in Cambridge to even know your neighbors."

That isn't to say that competition is completely absent from the darkened field. What does it mean to score a point when nobody's keeping track?

"It means we are better than them now," explained Stack, who dubbed her squad "Team Awesome."

The players usually get together after the game for ice cream at Herrell's, or, in last night's climate, a drink and a sandwich at a local bar. "It's a good way to get to know all the people you've been running around with," said co-organizer Jim O'Neill. "And to see their face in the light."

Last night, the destination was Charlie's Kitchen, an objective that was arrived at after some dithering. ("I'm not sure why anybody lets us in after frisbee, when we are all muddy and dirty," quipped Kelly Wilbur, who left the playing field with a glow stick tied in her hair.) The small diner could barely fit the large group of filthy twentysomethings, who squeezed into three booths in the back.

Group members took assessment of the night's play ("Nobody ran into any trees tonight," said Wilbur), and worried that last night's game would be the last until Spring. The cold temperatures were bearable, when you were running around, but difficult to handle when standing still. ("I'm cold now; can we play?" co-organizer Jim Chea had pleaded during a water break.) Talk turned to what would keep the group together during the off-season. Bowling, movies, and Wii parties. But, during the off months, there will be at least one player desperately longing to return to the muddy darkness of the Common.

"Frisbee is my life," claimed Amanda Maas.

The Illuminated Frisbee Nighttime Throwaround meets Tuesdays at 7:00pm on the Cambridge Common. Frisbee players of all levels and backgrounds are invited. Bring water, light-colored clothing (for visibility) and a dollar or two for equipment costs.

Image of illuminated frisbees from Meetup.com