A Hacky sack is a small bag filled with small pebbles or beads that is used to play a game with your feet. The object is to keep the Hacky sack in the air and off the ground for as many hits as possible and try to have everyone in the hack circle to hit it at least once. Once you are good enough you may attempt tricks such as behind the leg, around the world, stalls, ankle breaker, up and over, etc.
There are also a variety of other gmaes to play with a hacky sack such as

Killer Hack- a certain amount of people must touch the hack and then anyone can grab it out of the air and whip it at another person in the circle. If you are hit you are out for that game.

Power Hack- Everyone tried to hit the hacky sack as high into the air as possible, and make amazing saves to keep it going.

4 Square- Normally played with hands and a large ball that bounces, the rules are very similar but you play with a hacky sack and your feet. If you let the Hacky sack land in your square you are out and someone new comes in.

Hacky sack is a sociable game and can be thought of as a minor sport, no doubt that this game will eventually make it to the olypics as many irregular sports/games have. I dont know if there will be many competitors though because many hackyers are stoners, and you are not allowed drugs during the olympics.

Best time killing game ever invented and is very usefull when trying to fuck with teachers ect. at school.

a game played mostly by pot heads. if youre not a pot head but are good, get ready to be called a pot head. really a form a lazy man soccer. kick the bag, hope everyone in the circle hits the bag, if not, pick it up and try again. the ultimate time killer that doesnt get anwhere near as much respect as it deserves.

A tool used to get you assaulted and handcuffed by an officer for playing with while waiting for a train.

a hacky sack is a small bag, made of different fabrics, filled with beads or sand. the players try to keep it up by hitting it with their legs. a game that is usually played by stoners.

A great time killer at my school where we dont want to eat lunch or go into the commons with the damn preps. NOT JUST PLAYED BY POTHEADS!

a game that everyone can play, sept preps, cuz preps are fags.

the most kick ass past time in the world. when participating u use a small bag filled with sand or beads. you can hit the hacky sack with anything on your body except from ur elbows to your hands. the object of the game is to keep it from hitting the ground and trying to get everyone who is playin to hit the hacky sack at least once. if someone misses a perfectly playable ball, they get stiched by the person who hit it to them. stiching is where you get the hacky sack thrown at you as hard as the last person to hit it to you can throw it. after you dominate the art of getting hacks you can go freestyle and you can try getting stalls (where the hacky sack stops somewhere on your body, other than from your elbows to your hands, and you resume play after however long you want to keep the stall), and other cool moves such as kicking the ball alot of times by yourself until someone yells at you and tells you to pass.

played when bored with frustration of picking it up over again when miss kicking it.