Carton Rouge
In short
A red card is a penalty in football and other sports that forces a player to leave the pitch immediately. The player's team must continue the match with one fewer person on the field.
In plain words
When a player breaks a major rule or plays too dangerously, the referee shows them a red card. They are sent off the game and cannot be replaced by a substitute. This leaves their team at a disadvantage.
A simple example
A defender trips an attacker on purpose to stop a certain goal. The referee shows a red card, and the defender must go to the dressing room for the rest of the match.
Why it matters
It is the most severe punishment a referee can give during a game. It changes the balance of the match and often decides which team wins or loses.
Easy to mix up
Do not confuse it with a yellow card, which is a formal warning that does not force a player to leave immediately.