knickerbockers must cover their knees and teams began wearing them much shorter. They became known as "knickers", and were referred to by this term until the 1960s when "shorts" became the preferred term. Initially, almost all teams wore knickers of a contrasting colour to their shirts. In 1909, in a bid to assist referees in identifying the goalkeeper amongst a ruck of players, the rules were amended to state that the goalkeeper must wear a shirt of a different colour to their team-mates. Initially it was specified that goalkeepers' shirts must be either scarlet or royal blue, but when green was added as a third option in 1912 it caught on to the extent that soon almost every goalkeeper was playing in green. In this period goalkeepers generally wore a heavy woollen garment more akin to a jumper than the shirts worn by outfield players. Sporadic experiments with numbered shirts took place in the 1920s but the idea did not initially catch on. The first major match in which numbers were worn was the 1933 FA Cup Final between Everton and Manchester City. Rather than the numbers being added to the clubs' existing strips, two special sets, one white and one red, were made for the final and allocated to the two teams by the toss of a coin. The Everton players wore numbers 1–11, while the City players wore 12–22. It was not until around the time of the Second World War that numbering became standard, with teams wearing numbers 1–11. Although there were no regulations on which player should wear which number, specific numbers came to be associated with specific positions on the field of play, examples of which were the number 9 shirt for the team's main striker and the number 1 shirt for the goalkeeper. In contrast to the usual practice, Scottish club Celtic wore numbers on their shorts rather than their shirts until 1975 for international matches, and until 1994 for domestic matches. The 1930s also saw great advancements in boot manufacture, with new synthetic materials and softer leathers becoming available. By 1936 players in Europe were wearing boots which weighed only a third of the weight of the rigid boots of a decade earlier, although British clubs did not adopt the new-style boots, with players such as Billy Wright openly pronouncing their disdain for the new footwear and claiming that it was more suited