Red Cards

A red card is the heaviest punishment the referee can give to a player. The offender must leave the field at once, and he may well be banned for at least one further match. One he is gone, he cannot be replaced by a substitute; his team must continue with one less man. In the English Premier League there is an automatic three-match ban, although players can appeal against this.
Because they are so powerful, red cards are reserved for very bad behaviour such as violence, abuse or deliberate cheating. A red card can stain an entire team’s performance in a tournament, taking their players out of crucial games and sapping the morale of the squad.
The offences that warrant a red card are defined in FIFA’s Laws of the Game

1. Being guilty of ‘serious foul play’ (for instance, a very dangerous tackle).
2. Violence.
3. Spitting at an opponent or other person.
4. Denying the other side an opportunity to score by handling the ball.
5. Denying the other side an opportunity to score by fouling a player.
6. Offensive or abusive language or gestures.

Players frequently criticise the referee’s decision to ‘book’ them and it is quite ordinary for a yellow card to be upgraded to a red when they argue against his decision.
The system of coloured cards was invented in 1970 by a British Referee called Ken Aston, who came up with the idea while waiting at traffic lights on Kensington High Street.