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If you've watched any of the World Cup so far, you've probably noticed the curious white spray used by the refs during free-kicks.
Although it looks like shaving cream, it's really a non-toxic "vanishing spray" created by Argentine journalist Pablo Silva that will dissolve into the grass anywhere from 90-120 seconds after use. It caught on in South America in 2008, and is currently used in MLS. Next season, it will make its debut in the UEFA Champions League.
The reason for the vanishing spray is simple: on free kicks, the wall - the defenders lined up next to one another to guard part of the goal - must stand 10 yards from the ball. In the past, the ref had walked 10 yards from the ball and pointed vaguely to the place where the wall must stand, allowing the wall to creep back toward the ball to make it more difficult for the kick taker.
Now, with the vanishing spray, the refs can visibly mark 10 yards and ensure that the wall doesn't encroach on the play. It's a simple invention, but incredibly effective.
Here's a GIF of the vanishing spray from Mexico's 1-0 win over Cameroon.
ESPN