“Vanishing foam is a substance applied to an athletic field in order to provide a temporary visual marker. Its use in association football is not regulated by the Laws of the Game, authorisation being in the hands of the governing body of a match, league, or tournament. In association football, referees use the foam to enforce the rules as to the minimum distance that members of the opposing team must remain from the ball during a free kick, as well as the spot from which the kick is taken. …” Wikipedia