when was the yellow card introduced in football
Penalty card The idea of using language-neutral coloured cards to communicate a referee's intentions originated in association football, with English referee Ken Aston.[2] 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 – stop if safe to do so, red – stop) would transcend language barriers and make it clear that a player had been cautioned or expelled.[2] 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.
Substitute (association football) A player may only be substituted during a stoppage in play and with the permission of the referee. The player to be substituted (outgoing player) must have left the field of play before the substitute (incoming player) may enter the field of play; at that point the substitute becomes a player and the person substituted ceases to be a player. The incoming player may only enter the field at the half-way line. Failure to comply with these provisions may be punished by a caution (yellow card).