Footbag
A footbag is a small bean bag used as a ball in a number of sports. It is typically controlled by the feet but, in some sports, every part of the body except the hands and arms may be used. The term footbag is also the generic name for the sports which use the footbag. The main varieties are footbag freestyle, footbag net and circle kick. Both the footbag and the sports that use it are sometimes referred to as hacky sack (or hackey sack).
The same sport has also been practiced with a toy called a Koosh Ball.
Footbag freestyle
Footbag freestyle is a footbag sport where players demonstrate their abilities by performing sequences of difficult moves. The performance is judged for choreography, difficulty, variety and execution.
Footbag net
In footbag net, players (either playing for themselves, or with a partner) move a footbag back and forth across a five-foot-high net. This game combines elements of tennis, badminton, and volleyball. Specifically, the court dimensions and layout are similar to those of bandminton; the scoring is similar to old scoring system in volleyball (you must be serving to score); and serves must be diagonal, as in tennis. Footbag net games can be played to eleven or fifteen points, although the winners must win by at least two points.
Circle kick
Circle kick is the more common version of footbag, and is the game people are referring to when they talk about "hacking the sack" (or any other variant on the term "hacky sack"). In this game, players stand in a circle, do tricks with the footbag, and keep it moving around the circle. (TODO: add more info here, especially about variants, such as kill)
Equipment
Although some argue that a certain pair of shoes is necessary, the only piece of equipment that is really required in order to play footbag is a footbag. These come in many styles, colors, and varieties. Some footbags have simple cotton exteriors, while others are made of thirty to sixty panels of suede. Some are filled with sand; others, plastic pellets. Many footbags have designs on them, either geometric or pictorial (a happy face, for example). Some footbags are specialized for footbag net; these are generally not good for playing freestyle footbag.
Part of the appeal and popularity of footbag is due to this simplicity of equipment. A footbag can be bought for under $5, easily stored in a pocket, and later retrieved for a quick game of freestyle. Most other sports, by comparison, are not nearly as portable.
History of footbag
Footbag was conceived by John Stalberger and Mike Marshall in Oregon City, Oregon in 1972. They coined two terms: "hacky sack", which referred specifically to their product, and "footbag", which is the generic name for the game and the product. "Hacky sack" is now trademarked by Wham-O, and should technically not be used to refer to the game or the bean bag, but almost always is.