A footbag is both a small, round bag, and the term for the various sports played with one – characterized by controlling the bag by using one's feet. Although often referred to generically as a Hacky Sack, that is the trademarked name of one specific brand.
Footbag-like activities have existed for many years. There are documented examples like Wu Style Tai Chi Chuan practice and policemen are seen playing it using a shuttlecock in the 1955 movie To Catch a Thief, but the current Western incarnation of the sport was invented in 1972 by Mike Marshall and John Stalberger of Oregon City, Oregon with the Hacky Sack, the rights to which are now owned by Wham-O.
For circle kicking, it is very common to use a crocheted footbag, which is usually filled with plastic beads. Casually, footbags are often differentiated as normal (indicating a plastic-pellet filling), or as "dirt bags" or "sand hacks" (indicating a sand filling). Sand hacks are typically considered ideal among casual, beginning, or intermediate players, who use them as a learning tool, as they are easier to control and stall than a crocheted bag filled with plastic pellets.
In the freestyle footbag discipline, a 32 panel bag is the generally accepted standard (the number of panels on commercially available bags can range from 2 to 120 panels). Stitchers generally use Plastic Poly Pellets, sand, BB's, steel shot, lead shot, seed bead, or tungsten shot as filler. Most professional stitchers use a custom combination of different fillers to make the bag play better. Bags usually weigh between 40 and 65 grams, depending on the type of filler and amount of filler used. 32 panel bags do not stall as easily as a "dirt bag" or "sand hack," but set truer from the foot, allowing for more complex tricks. Professional footbags are usually made out of the fabrics ultrasuede light, facile, or amaretta. While these bags can last a long time with proper care, they are quite fragile relative to their more common crocheted cousins.
The footbag net discipline uses a distinct bag, characterized by a harder outer surface than other footbags. These bags are not suitable for freestyle, and vice versa.