Yellow and red cards are part of the disciplinary system in soccer games at all levels. The yellow card is given for minor offenses and deemed a first warning. The red card is given for more serious incidents or for repeatedly bad behavior. In high school soccer, a red card could mean missing several weeks of soccer matches, whereas in professional soccer the player will miss a set amount of games.
Two yellow cards equal a red card. Yellow cards are given to players for any one of these reasons: unsporting behavior, dissent by word or action, time-wasting, a series of fouls, failing to retreat the required distance, entering the pitch without permission of the referee and leaving the pitch without the referee's permission. In high school soccer, the second yellow will be shown with a red in the same hand. In professional soccer, the yellow and red are shown sequentially.
A player is shown a straight red card for any one of these reasons, notes the BBC website: a dangerous tackle, violent conduct like punching, deliberate handball stopping a goal, spitting at another person, using offensive language or gestures toward another person, deliberately fouling a player when you are the last defender in front of the goal, and two yellow cards. The referee will raise the card and point the player off the pitch.
Any player of the team or coaching staff can be given yellow or red cards. The coach, training staff and substitutes can be given these cards from the sidelines. As Alabama High School Soccer Coaches Association notes, a sent off player must leave the playing field but can stay in the substitutes area. This is different compared to professional soccer, where the player must leave the playing vicinity completely.
The consequences of losing a player are the same for high school and professional soccer. The player cannot be replaced, and the team must therefore play on with 10 players rather than 11. If the coach is sent off, the coach can relay tactics to the assistant coach, or the assistant coach will take over all duties for the remainder of the game. The sent-off player also receives a suspension of at least one additional game.