In association football, kit (also referred to as a strip or uniform) is the standard equipment and attire worn by players. The sport's Laws of the Game specify the minimum kit which a player must use, and also prohibit the use of anything that is dangerous to either the player or another participant. Individual competitions may stipulate further restrictions, such as regulating the size of logos displayed on shirts and stating that, in the event of a match between teams with identical or similar colours, the away team must change to different coloured attire.
Footballers generally wear identifying numbers on the backs of their shirts. Originally a team of players wore numbers from 1 to 11, corresponding roughly to their playing positions, but at the professional level this has generally been superseded by squad numbering, whereby each player in a squad is allocated a fixed number for the duration of a season. Professional clubs also usually display players' surnames or nicknames on their shirts, above (or, infrequently, below) their squad numbers.
Football kit has evolved significantly since the early days of the sport when players typically wore thick cotton shirts, knickerbockers and heavy rigid leather boots. In the twentieth century, boots became lighter and softer, shorts were worn at a shorter length, and advances in clothing manufacture and printing allowed shirts to be made in lighter synthetic fibres with increasingly colourful and complex designs. With the rise of advertising in the 20th century, sponsors' logos began to appear on shirts, and replica strips were made available for fans to purchase, generating significant amounts of revenue for clubs.
The Laws of the Game set out the basic equipment which must be worn by all players in Law 4: The Players' Equipment. Five separate items are specified: shirt (also known as a jersey), shorts, socks (also known as stockings), footwear and shin pads. Goalkeepers are allowed to wear tracksuit bottoms instead of shorts.
While most players wear studded football boots ("soccer shoes" or "cleats" in North America), the Laws do not specify that these are required. Shirts must have sleeves (both short and long sleeves are accepted), and goalkeepers must wear shirts which are easily distinguishable from all other players and the match officials. Thermal undershorts may be worn, but must be the same colour as the shorts themselves. Shin pads must be covered entirely by the stockings, be made of rubber, plastic or a similar material, and "provide a reasonable degree of protection". The only other restriction on equipment defined in the Laws of the Game is the requirement that a player "must not use equipment or wear anything that is dangerous to himself or another player".
It is normal for individual competitions to specify that all outfield players on a team must wear the same colours, though the Law states only "The two teams must wear colours that distinguish them from each other and also the referee and the assistant referees". In the event of a match between teams who would normally wear identical or similar colours the away team must change to a different colour. Because of this requirement a team's second-choice is often referred to as its "away kit" or "away colours", although it is not unknown, especially at international level, for teams to opt to wear their away colours even when not required to by a clash of colours, or to wear them at home. The England national team sometimes plays in red shirts even when it is not required, as this was the strip worn when the team won the 1966 FIFA World Cup. Many professional clubs also have a "third kit", ostensibly to be used if both their first-choice and away colours are deemed too similar to those of an opponent. Most professional clubs have retained the same basic colour scheme for several decades, and the colours themselves form an integral part of a club's culture. Teams representing countries in international competition generally wear national colours in common with other sporting teams of the same nation. These are usually based on the colours of the country's national flag, although there are exceptions—the Italian national team, for example, wear blue as it was the colour of the House of Savoy, the Australian team like most Australian sporting teams wear the Australian National Colours of green and gold, neither of which appear on the flag, and the Dutch national team wear orange, the colour of the Dutch Royal House.
Shirts are normally made of a polyester mesh, which does not trap the sweat and body heat in the same way as a shirt made of a natural fibre. Most professional clubs have sponsors' logos on the front of their shirts, which can generate significant levels of income, and some also offer sponsors the chance to place their logos on the back of their shirts. Depending on local rules, there may be restrictions on how large these logos may be or on what logos may be displayed. Competitions such as the Premier League may also require players to wear patches on their sleeves depicting the logo of the competition. A player's number is usually printed on the back of the shirt, although international teams often also place numbers on the front, and professional teams generally print a player's surname above his number. The captain of each team is usually required to wear an elasticated armband around the left sleeve to identify him as the captain to the referee and supporters.