Squad numbers are used in association football to identify and distinguish players that are on the field. Numbers very soon became a way to also indicate position, with starting players being assigned numbers 1–11, although in the modern game they are often influenced by the players' favourite numbers and other less technical reasons, as well as using "surrogates" for a number that is already in use. However, numbers 1–11 are often still worn by players of the previously associated position.

The goalkeeper is a position in association football. It is the most specialised position in the sport. The goalkeeper's main role is to stop the opposing team from scoring. This is accomplished by having the goalkeeper move into the trajectory of the ball to either catch it or direct it further from the vicinity of the goal line. Within the penalty area goalkeepers are allowed to use their hands, giving them the sole rights on the field to handle the ball. The goalkeeper is indicated by wearing a different coloured kit from their teammates and opposition.