Hack slap is a game that utilises a footbag or 'Hacky Sack'.
The game is similar to the Australian handball rules.
The object is to keep the 'footbag' in the air by any means necessary, excluding hands.
Similar to tennis, when a player wins a rally, they receive a point.
The other method of play when the game is down to the final four competitors is referred to a 'Normals' or 'Fatal Four Way'.