Goalkeeper in association football is one of the four positions in the game. It is arguably considered the most important position in the sport. The goalkeeper's main job is to stop the other team from getting the ball over the goal-line (between the posts and under the crossbar. Goalkeepers normally do this by catching, punching or egg-beating the ball away. Because of this the goalkeeper is the only player allowed to use his hands but is forbidden to do so outside the penalty area. Goalkeepers also give commands to their defense during corners, free kicks as well as marking. Goalkeepers can also tell their team mates where to go go in attack.
Goalkeepers are required to remain on the pitch at all times though that does not mean they have to be between the sticks all the time. For example goalkeepers may have to take a penalty during a penalty shoot-out or even go for a corner late in the game though it is rare, as it leaves the goal unguarded. If a goalkeeper is hurt or sent off the back-up goalkeeper must take his place, if not then an outfielder must do so. In the event of a sending off an outfielder too must leave and the other keeper "replaces" him. If both keepers are hurt or sent off and there is no third choice keeper especially at club level, an outfielder (usually a defender) has to take his place and wear the goalkeeper kit. Because goalkeeper is the most important job in football as well as being the most difficult position to master, most teams have the same keeper play in the starting XI every season. For example Petr Cech is currently no.1 at Chelsea while Iker Casillas has been Real Madrid's no.1 for more than 9 years. As a result it could be a long time before the back-up keeper has a chance to play. This is one of the main reasons why most goalkeeper on average retire in their forties. The main squad number for a goalkeeper is no.1 but today though this is still common some goalkeepers now wear other squad numbers when in goal. For example despite being no.1 at Liverpool Pepe Reina has worn the no.25 jersey through all his Liverpool career. No.13 especially in Britain is the common number for the second choice keeper, though others like 16 are 25 and also common.