A penalty card is used in many sports as a means of warning, reprimanding or penalising a player, coach or team official. Penalty cards are most commonly used by referees or umpires to indicate that a player has committed an offense. The referee will hold the card above his or her head while looking or pointing towards the player that has committed the offense. The colour and/or shape of the card used by the official indicates the type or seriousness of the offence and the level of punishment that is to be applied.

By analogy the term is sometimes used in other areas than sport. For example, the UK Radio Authority speaks of issuing a yellow card to those who break its rules.

The idea of using language-neutral coloured cards to communicate a referee's intentions originated with British football referee Ken Aston. Aston had been appointed to the FIFA Referees' Committee and was responsible for all referees at the 1966 FIFA World Cup. In the quarter finals, England met Argentina at Wembley Stadium. After the match, newspaper reports stated that referee Rudolf Kreitlein had cautioned both Bobby and Jack Charlton, as well as sending off Argentinian Antonio Rattin. The referee had not made his decision clear during the game, and England manager Alf Ramsey approached FIFA for post-match clarification. This incident started Aston thinking about ways to make a referee's decisions clearer to both players and spectators. Aston realised that a colour coding scheme based on the same principle as used on traffic lights (yellow - caution, red - stop) would traverse language barriers and clarify whether a player had been cautioned or expelled. As a result, yellow cards to indicate a caution and red cards to indicate an expulsion were used for the first time in the 1970 FIFA World Cup in Mexico. The use of penalty cards has since been adopted and expanded by several sporting codes, with each sport adapting the idea to its specific set of rules or laws.

Kieran James Ricardo Gibbs (born 26 September 1989) is an English footballer who plays for Arsenal and was a product of their academy who came to prominence during 2006–07 FA Youth Cup by scoring in the semi-final prior to his first-team breakthrough. He plays as a left back for Arsenal and made his début for the Senior England national team in a friendly against Hungary at Wembley Stadium on 11 August 2010. He attended Riddlesdown High School in Purley, London.

Gibbs began his career at the Wimbledon academy but moved to Arsenal along with Abu Ogogo and James Dunne when Wimbledon disbanded in 2004 and became Milton Keynes Dons. He played in the centre midfield position and also on the left wing. He has featured regularly for Arsenal's U18 and reserves teams and also played in pre-season friendlies against Barnet and Inter Milan.

In September 2007, Gibbs signed a professional contract with Arsenal, and was named in the club's 2007–08 UEFA Champions League squad and given squad number 34. He made his first-team debut for the club when he started a League Cup match against Sheffield United on 31 October 2007, and made his second appearance coming on as a substitute for Eduardo da Silva in Arsenal's quarter-final against Blackburn Rovers on 18 December 2007.

Eden Hazard (born 7 January 1991) is a Belgian international footballer who currently plays for French club Lille in Ligue 1 and the Belgium national team. He primarily plays as an attacking midfielder and a winger. Hazard is known for his creativity, speed, and technical ability and is described as a "fearless, explosive attacking midfielder who can change the game with a turn of pace or a dribble". He has also been described as "a defender's nightmare" and has earned critical acclaim for his playing style, which has led to the media, coaches, and players drawing comparisons to FIFA World Player of the Year winners Lionel Messi and Cristiano Ronaldo.

Hazard is the son of former Belgian footballers and began his football career in Belgium playing for local clubs Royal Stade Brainois and Tubize. In 2005, he moved to France joining first division club Lille. Hazard spent two years in the club's academy and, at the age of 16, made his professional debut in November 2007. In his first full season as a starter, he won the National Union of Professional Footballers (UNFP) Young Player of the Year award becoming the first non-French player to win the award. In the 2009–10 season, Hazard captured the award again becoming the first player to win the award twice. He was also named to the league's Team of the Year. Since making his debut in 2007, Hazard has become an integral part of the club under manager Rudi Garcia racking up over 190 appearances. In the 2010–11 season, he was a part of the Lille team that won the league and cup double and, as a result of his performances, was named the UNFP Ligue 1 Player of the Year becoming the youngest player to win the award. Hazard was also given the Bravo Award by Italian magazine Guerin Sportivo for his performances during the 2010–11 season.

Arda Turan (born 30 January 1987) is a Turkish footballer who plays for Atlético Madrid and the Turkish national team, as a left winger. At the age of 22, prior to the 2009–10 season he was made the captain of Galatasaray.

Arda already has 50 senior national caps and 12 goals for Turkey, and following a successful Euro 2008 campaign, he was ranked 8th in a selection of the 100 Best Young Football Players in the World, published by Spanish magazine Don Balón in July 2008. In January 2011, Arda was voted as the third most popular European footballer of 2009, and the 14th most popular footballer in the world, by the IFFHS.

Arda is a product of the Galatasaray youth. He was promoted to first team by Gheorghe Hagi in 2004–05 season, making his official debut against Bursaspor in a Turkish Cup match on 22 January 2005. He had a spell on loan to fellow Super Lig side Manisaspor in the second half of the 2005–06 season. He was recalled the for the start of the following 2006–07 season, and quickly broke into the first team. It was during this time that he received his first senior international call up. Arda helped Galatasaray to qualify to the Champions League group stage.

Iker Casillas Fernández (Spanish pronunciation: [ˈikeɾ kaˈsiʎas feɾˈnandeθ]; born 20 May 1981) is a Spanish football goalkeeper who plays for the Spanish La Liga club Real Madrid and the Spanish national team, being the captain of both. In 2008 he led the Spanish national team to their first European Championship in 44 years, and in 2010 to win the World Cup, Spain's first ever, being also named the tournament's best goalkeeper.

Casillas has been nominated for the European Footballer of the Year award twice, ranking fourth overall in 2008 and again receiving more votes than any other goalkeeper in 2009. At the end of 2009 he was voted into the UEFA Team of the Year for the third consecutive time. As of 2011 Casillas is one of a very select group of players who have won all major club and national championship titles. In 2010, he was awarded with the Sports Prince of Asturias Award. On 19 October 2010, Casillas became the most capped goalkeeper of all time in the UEFA Champions League and in November 2011, he became the most capped player of all time for the Spanish national team.