Goalball competitions are set apart from all other Paralympic events due to the unique atmosphere inside the playing venue. The object is to roll the ball into the opponent's goal while the opposing players try to block the ball with their body. Bells inside the ball help to orient the players indicating the direction of the on-coming ball. Therefore, while play is in progress, the gymnasium is completely silent so as to allow the players to concentrate and react instantly to the ball. Goalball is played by male and female athletes who are visually impaired and wear "blackout" masks to ensure that all participants are competing equally. Each team has three players on the court and a maximum of three substitutes. It is exclusively a sport for athletes with a visual impairment and was introduced to the world in 1976 at the Paralympics in Toronto. All competitors wear goggles while they are on the playing court, which allows athletes with varying degrees of vision to participate together. The governing body of Goalball is the International Blind Sport Federation (IBSA) and the sport is currently played in around 51 countries worldwide.