Five-a-side football is a variation of association football in which each team fields five players (four outfield players and a goalkeeper). Other differences from football include a smaller pitch, smaller goals, a reduced game duration. Matches are played indoors, or outdoors on AstroTurf or artificial grass pitches that may be enclosed within a barrier or "cage" to prevent the ball from leaving the playing area and keep the game flowing.
The penalty area is significantly different from football: it is semi-circular in shape, only the goalkeeper is allowed to touch the ball within it, and he or she may or may not be allowed out. Goalkeepers are only allowed to give the ball out to another player through hands. The goalkeeper may only kick the ball if it is in the course of making a save. There are no offside rules. Headers are allowed. No protocol of deliberate handball vs accidental handball - referee needs to make a decision based on the distance from where the ball was hit. Yellow cards may result in the offending player being sent to the "sin bin" for a predetermined length of time. Red cards work in the same way as the 11-a-side game. Charging/sliding tackles are awarded a yellow card.
Additionally, metal studded boots or blades cannot be worn, as it damages the playing surface. Players are also required to wear shin guards but this is usually at the discretion of the referee.
Five-a-side is commonly played informally, and the rules are therefore flexible and are sometimes decided immediately before play begins; this is in contrast to futsal, for which official laws are published by FIFA.
The English FA have drawn up a full list of laws for the small-sided game which expands upon the rules outlined above and includes minimum/maximum pitch dimensions as well as technicalities on free-kicks and other parts of the game.
Futsal is a version of indoor five-a-side football developed by the Asociación Mundial de Fútbol de Salón (AMF / English:World Futsal Association). It currently has two governing bodies: Asociación Mundial de Fútbol de Salón, and the Fédération Internationale de Football Association (FIFA).