The red card is a tiny object used in the Muggle world in football matches. In 1991 Dean Thomas yelled that one of the Quidditch players on Slytherin Quidditch team should be given a red card for knocking out Harry Potter. Ron Weasley told him that such an object doesn't exist. A Red Card was the term the crew used on set with the actors to get them to stop messing up.
- Harry Potter and the Philosopher's Stone (Mentioned only)