What card is shown for serious foul play?

The card shown for serious foul play is a red card. This card is used to indicate that a player has committed an offense that is considered to be particularly severe, such as a reckless challenge that endangers the safety of an opponent. When a referee issues a red card, it results in the immediate dismissal of the player from the match, signifying the gravity of the foul.

In contrast, yellow cards serve as a caution for less severe fouls or misconduct, such as unsporting behavior or persistent infringement of the rules. The green and blue cards are not standard cards used in most football (soccer) competitions; they either represent alternative disciplinary tools in different sports or specific leagues but do not apply in this context. Thus, a red card being used for serious foul play aligns with the regulations set forth by the laws of the game.