Knocking over another player without making a play for the ball will likely result in the referee calling a foul in soccer, and perhaps issuing a yellow card as a warning to you or a red card to eject you from the game. The rules of FIFA, soccer's governing body, work to limit extremely hard tackles that might injure players and specify additional offenses that could lead to a foul call. Referees, coaches, strikers and most especially defenders need to know the fine points of when fair challenges, as both players contest the ball, cross the line into a foul that will result in a referee's whistle.
Elements
FIFA's Laws of the Game contain Law 12, Fouls and Misconduct, defining actions that can result in a foul call. These include kicking or tripping an opponent, jumping or charging an opponent and striking, pushing or tackling or attempting to strike another player. These infractions result in the award of a direct free kick to the team that suffered the foul, or a penalty kick if the offense is committed by a player inside her own penalty area. Holding an opponent is not a foul, but is an offense that also results in a direct free kick to the other team. The kick originates from the spot of the offense.
Exceptions
Players are permitted to attempt to take the ball away from other players, generally by tackling, which in soccer terms refers to a poke of the ball with your foot, a block with your ankles or a full-body slide to redirect the ball to your possession. If a player uses his shoulder to nudge a dribbler off the ball to steal it, without extending elbows or hips or going through the dribbler's body or legs to get the ball, no foul has occurred even if the dribbler falls down in the course of the tackle.
Cards
The referee can award a yellow card for offenses that rate a warning. The card serves as notice that a player is at risk of being sent off if he repeats the offenses. Reasons include unsportsmanlike behavior, dissent and persistent infringement of the Laws of the Game, including repeated fouling. The referee can award a red card for serious foul play, violent conduct, spitting at an opponent or any other person or denying an obvious goal-scoring opportunity to an opponent by fouling. A player who receives a red card must leave the field of play. A second yellow card also can result in removal from the game.
Play Advantage
The referee may choose not to call a foul in certain circumstances to allow a goal-scoring opportunity to develop for the player or team that was fouled. For example, if a player hurdles an attempted trip, stays on her feet despite a hard tackle or otherwise shrugs off a clear foul and continues dribbling or passing effectively, the referee may "swallow his whistle" and allow play to continue to avoid penalizing the team with the ball. The Laws of the Game call for the referee to honor play advantage when there is "the chance of an immediate, promising attack." The referee may wait until a stoppage in play or the thwarting of the attack to stop play and then penalize a team for the original offense.



Member Comments