Law 4 of the Laws of the Game, written by the International Football Association Board (IFAB), sets out what players must wear, what they may add and what is forbidden. Match pages on RubiScore record every caution in a match timeline, and a small number of those cautions each season come from this short, often overlooked law.
This listicle covers nine things Law 4 says, from the five compulsory items to jewellery, colours, lost boots, slogans and wearable tracking devices, followed by what the law leaves to competition rules. Match and referee data are available at https://rubiscore.com for readers who want to see how officials apply the Laws in practice.
Law 4 has two purposes: safety and clarity. Equipment must not endanger the wearer or anyone else, and kit must allow the referee, the other officials and the players to tell the teams apart at a glance. Almost every detail in the law, from the colour of undershorts to the ban on rings, follows from one of those two principles.
The law applies to every match played under the Laws of the Game. Competitions then add their own regulations on top, covering matters such as shirt numbers, names and advertising, which is why kit rules can look different from league to league even though Law 4 is the same everywhere.
Every player must wear five separate items: a shirt with sleeves, shorts, socks, shin guards and footwear. The list is short but strict. A sleeveless shirt does not comply, and a player cannot take part without shin guards.
Shin guards must be made of a suitable material that gives reasonable protection, and they must be covered by the socks. The law does not prescribe a minimum size, which is why some professionals wear very small guards. The requirement is that they are present, protective and covered.
Players often wear base layers and compression shorts, and the law controls their colours. Undershirt sleeves must be the same main colour as the shirt sleeve or a pattern or colour that exactly replicates it. Undershorts and tights must be the same colour as the main colour of the shorts or of the lowest part of the shorts.
Teammates must also match each other. Players of the same team wearing undershorts or tights must all wear the same colour, so one player cannot wear black while another wears white.
Players commonly tape their socks or wear sock sleeves. Any tape or other material applied or worn externally must be the same colour as the part of the sock it is applied to or covers. A white strip of tape around a red sock is therefore not permitted.
This detail is one of the clearest illustrations of the clarity principle. Small differences in colour are not a safety issue, but the law treats kit as a single visual identity for each team.
All jewellery is forbidden. That includes necklaces, rings, bracelets, earrings, leather bands and rubber bands, and the items must be removed. Covering jewellery with tape is not permitted. The rule exists because jewellery can injure the wearer or another player in a collision.
Match officials are also prohibited from wearing jewellery, apart from a watch or similar device used for timing the match. A player who refuses to remove an item, or puts it back on during the match, can be cautioned.
The two teams must wear colours that distinguish them from each other and from the match officials. Each goalkeeper must wear colours that distinguish him or her from the other players and from the match officials. If both goalkeepers' shirts are the same colour and neither has another shirt, the referee can allow the match to be played.
Goalkeepers have some extra freedom. They may wear tracksuit bottoms and a cap, and protective gloves are standard. Colour clashes between teams are normally avoided well before kick-off through competition kit approval, but the final judgement rests with the referee on the day.
Non-dangerous protective equipment is permitted: headgear, facemasks, knee and arm protectors made of soft, lightweight padded material, and sports spectacles. Head covers, other than goalkeepers' caps, must be black or the same main colour as the shirt, must be professional in appearance, must not be attached to the shirt and must not have any part extending from the surface.
These conditions allow players to wear religious head covers or protective headgear after injury, while preventing designs that could catch on an opponent or create a danger in a challenge.
If a player accidentally loses footwear or a shin guard, it must be replaced as soon as possible and no later than when the ball next goes out of play. If, before doing so, the player plays the ball or scores a goal, there is no offence and the goal is awarded, because the loss was accidental.
The situation is different when equipment is dangerous or incorrect. A player can be told to leave the field to correct it and must not return without the referee's permission. The referee, or another match official, checks the equipment before the player re-enters, and re-entry normally happens when the ball is out of play. A player who comes back on without permission can be cautioned.
Compulsory equipment must not carry any political, religious or personal slogans, statements or images. Players must not reveal undergarments showing slogans or advertising beyond the manufacturer's logo. The law leaves the sanction to the competition organiser, the national association or FIFA, rather than to the referee during the match.
That is why players are sometimes disciplined after a match for a message on a T-shirt revealed during a goal celebration. Removing the shirt itself is a separate matter, covered by the law on misconduct, which makes it a cautionable offence.
Many teams now use electronic performance and tracking systems (EPTS) to measure distance, speed and workload. Law 4 permits wearable devices that form part of such a system, provided they are safe and, in official competitions, meet the approved quality standard set out in the Laws.
The same law covers electronic communication. Players may not use communication devices during the match, while team officials in the technical area may use small handheld devices for coaching or player welfare. Live tracking data therefore reaches the bench, not the players on the pitch.
Several familiar kit rules are not part of the Laws of the Game at all:
This division explains why kit rules seem to vary between leagues. The Law sets the safety and clarity minimum; competitions add identity and commercial rules on top.
Equipment issues rarely make headlines, but they appear in match records. A caution for re-entering the field without permission, for refusing to remove jewellery or for removing a shirt in celebration is logged like any other booking. Referee card statistics, such as those on RubiScore, count these technical bookings alongside cautions for fouls or dissent, so a referee's total can include a few that say nothing about how strictly he judges challenges.
For players and coaches, the practical message is simple: Law 4 is checked before kick-off, but it applies throughout the match. Getting the small details right — tape colour, base layers, jewellery — avoids delays and cautions that have nothing to do with how the game is played.