"Impeding the Progress of an Opponent" is an "Indirect Kick Foul" in soccer (see "Fouls, Indirect Kick, Impeding The Progress Of An Opponent"). This used to be called "obstruction". Generally, a player cannot use his body to impede another player's movements, even if it is not deliberate. This can be called if a player is not within "playing distance" of the ball (i.e., 3 feet) and block's an opponent's movement or screens an opponent from the ball. However, if a player is within playing distance & able to play the ball (meaning not laying on the ground), the player can legally screen an opponent from the ball. (You usually see this when a ball is going out of bounds & the player whose team will get the throw-in screens the opponent so the opponent can't save the ball). The rule also applies to "innocently" impeding the goalkeeper by standing in front of him when he has the ball.
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