Bar none: Ultimate Frisbee.
Sometimes referred to as "Frisbee Football," Ultimate is a healthy, vigorous team sport that combines elements of soccer, football, and lacrosse to create a one-of-a-kind athletic experience. It's fun, fast, friendly, and furious. Like chess, the rules are simple and the possibilities endless.
The Ultimate field is 70 yards x 40 yards, containing two endzones, each 25 yards deep. There are 7 players per team, or, lacking 14, half as many as are available. In what is called the "pull," the defense throws out the disc to the offensive team, and play begins.
Players advance the disc down the field by passing it between themselves. It is illegal to run or "travel" with the disc. If a pass is intercepted or incomplete, a "turnover" occurs, and the other team assumes possession of the disc. A point is scored when a team successfully completes a pass into their respective endzone.
One unique feature of the game is that it is self-moderated - players resolve disputes about fouls or scoring among themselves. Literature about the sport often emphasizes the "Spirit of The Game," which, although it sounds a bit wooly on the surface, is quite an admirable creed.
Grab a disc and make it brisk. This is DA GAME! or, *ahem,* a most exquisite exercise, if you prefer.
Image courtesy of riversideultimate.com