The goalkeeper, often shortened to keeper or goalie, is one of the major positions of association football. It is the most specialised position in the sport. The goalkeeper's primary role is to prevent the opposing team from scoring (moving the ball over the defended goal-line within the frame of the goal). This is accomplished by the goalkeeper moving into the path of the ball and either catching it or directing it away from the vicinity of the goal line. Within the penalty area goalkeepers are able to use their hands, making them (outside throw-ins) the only players on the field permitted to handle the ball. The special status of goalkeepers is indicated by them wearing different coloured kits from their teammates. The back-pass rule prevents goalkeepers handling direct passes back to them from teammates. Goalkeepers usually perform goal kicks, and also give commands to their defence during corner kicks, direct and indirect free kicks, and marking. Goalkeepers play an important role in directing on field strategy as they have an unrestricted view of the entire pitch, giving them a unique perspective on play development. The goalkeeper is the only required position of a team. If they are injured or sent off, a substitute goalkeeper has to take their place, otherwise an outfield player must take the ejected keeper's place in goal. In order to replace a goalkeeper who is sent off, a team usually substitutes an outfield player for the backup keeper (thus effectively the red card and substitution takes out two of the starting eleven players). They then play the remainder of the match with nine outfield players. If a team does not have a substitute goalkeeper, or they have already used all of their permitted substitutions for the match, an outfield player has to take the dismissed goalkeeper's place and wear the goalkeeper shirt. The squad number for a first choice goalkeeper is generally number 1, although they may wear any jersey number between 1 and 99.