Hacky sack
Hacky Sack is the trademarked name of a type of footbag. The name "hacky sack" came from the inventors of the footbag, John Stalberger and Mike Marshall. Marshall suffered a fatal heart attack in 1975, however Stalberger continued the business. At a later date, Stalberger sold the title to Wham-O. The name Hacky Sack has become a genericized trademark.
Circle Kicking
Hacky Sack is sometimes also referred to as Circle Kicking. There is a formal game of footbag but Hacky Sack is played informally, with little or no rules. Hacky Sack generally consists of a group of people formed in a circle, trying to keep the footbag in the air. Usually the goal of the game is to complete a "hack". A "hack" is when the footbag is passed around and touched by every player in the circle, without touching the ground. Many players feel the game is based on respect and fun, so someone showing off and kicking to yourself is generally frowned upon.
Other games are also played, for example, waterfall, kill, step up and tower. There is also Slaps:
Slaps is when there is a certain number of kicks between a certain number of people, once this is accomplished the hacky sack can be slapped at a member of the group and if the hack hits the person or anyone else they are either eliminated until there is one person left or they have an out if they are playing with more then 1 out. The rule might be 5 between 3 so there most be 5 total hacks between 3 people before the hacky sack can be slapped at a member of the circle. It is a survival game the last one standing wins the round. Usually when it gets down to 2 people there will be a hack off; where the winner is determined by the number of consecutive hacks they can do the one with the most consecutive hacks wins the game.