In soccer, a yellow card is typically shown for a serious foul that warrants a warning to the player. However, for more serious offenses or violent conduct, a red card is issued, resulting in the player's expulsion from the game. The card system helps enforce discipline on the field, allowing referees to manage player behavior and maintain fairness during matches. Players must be cautious, as accumulating two yellow cards in a game results in a red card, leading to ejection from the match.