What is the 'vanishing spray' used in FIFA World Cup 2014?

For those unaware of how it's used, the referee will spray it on the ground around the ball and in front of the wall on free kicks to ensure that the wall doesn't encroach on the set-piece taker. And almost just as quickly as the spray is used, it's gone, leaving no lasting effect on the pitch.

You see it all the time on free kicks: Once the referee is done putting the wall in place, in unison, the wall collectively moves forward inch by inch.

That closes down the angle with which the set-piece taker can operate. Most of the time, he can't fire the ball over the wall without overshooting his intended target as a result.

In theory, vanishing spray should eliminate that problem altogether. In practice, that's an unrealistic goal. Vanishing spray should at least keep the wall more honest.

"It will assist us in getting the players back at a free kick and, in turn, that gives the attacking team a better opportunity of creating something from that set-piece," English referee Howard Webb said, per BBC Sport's Luke Reddy.

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