Blind football (or five aside football) is a palalympic adaptation of regular football for those who are visually impaired or completely blind. It was developed in Spain with the first Spanish National Championships being held in 1986. It was introduced to the paralympic games in 2004. Not surprisingly Brazil and Argentina have dominated the world championship that started in 1998.
It is set-up similar to indoor football, with a smaller 42m by 22m field surrounded by boards. Because of this there are not throw-ins. The teams have five members of which the goalie may be sighted (but is restricted to the goalie area). There is also a sighted member, called a guide, on the sidelines who is allowed to call out. Because there are varying levels of sightedness all players, except for the goalie, must wear eye-patches or blindfolds. Padding is also worn for the inevitable collisions. The ball itself isn't the usual ball but normally contains ball bearings that make noise when it moves as well as being smaller (size three) and less bouncy.
When you are approaching to take the ball off another player you must call out "Voy!", meaning "Go" in Spanish. In addition to this players will also have to deal with calls from the guide as well as other players. It isn't surprising that the audience are often quieted when too loud. Other sources of noise pollution can be a problem, such as overhead planes, which may require the referee to stop play.
Blind football is often described as being surprisingly fast-paced and gritty. To watch the sport is amazing. Watching the tricks and skills of mainstream professional football is impressive but to watch the people do the same while blind blows me away. Here is a clip from the 2010 IBSA World Blind Football Championship which will show you what I mean. There are a few points where they misjudge where the goal is (example at 1:40) and once a player looses where the ball is (about 2:00 in) but that is nothing given that they are dealing with the challenge of not being able to see. Without the benefit of sight the players have to figure out other ways of getting the same information that a sighted player would.