UltimateFrisbee is a sport played with 14 people, a large field, a flying disc and enthusiasm.

It's a little like a cross between soccer and american football with a frisbee. Once you catch the disc you can't run with it, you have to pass it to a team-mate. The goal is to catch the disc in the end-zone for a point.

The official rules for most tournament play are found at the UPA (Ultimate Players Assoc) website, which is the national organization for organized ultimate.  http://www1.upa.org/ultimate/rules -- AndrewFischer

the official system of calling and contesting fouls is quite unique among sports. Basically the game has no referees, and relies on the honour system. In friendly games players often call fouls on themselves.

Primarily ultimate finds its routes in university settings, which is where many veteran players are exposed to it, but many cities also have summer leagues and pickup games. -- RonGarcia

I played it a few times in college with a bunch of my engineering buddies.  It's definitely good exercise, yet (can be) light enough impact even for the stereotypical geek fitness level. 

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Ultimate is an incredibly fun team sport.  Co-ed teams are common, which goes a long way to dampen the testosterone factor in competitive sports.  The game is engaging, friendly, and '''fun'''.  There aren't any referees; players adhere to the ''spirit of the game''.  I feel it inspires interactive social interaction.  For more information about the sport, check out these links:

* Ultipedia: a wiki dedicated to the sport - http://www.ultipedia.org/
* Ultimate Players Association - http://www.upa.org/
* Ultimate in Seattle - http://www.discnw.org/
* Ultimate in IndianapolisIndiana - http://indyultimate.danconia.org/
* Ultimate in Great Britain - http://www.ukultimate.com/

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The Ultimate Co-Ed Sport for White People: http://stuffwhitepeoplelike.com/2008/02/14/67-co-ed-sports/?cp=all (including comments).

Another hippie sport: Frisbee Golf.