There is a graphic design element to tennis courts, (American) football fields and basketball courts, with highly visible lines indicating boundaries and distances. These are fixed in place, as service lines, end zones and free throw lines aren't meant to move.
Soccer, though, has a unique problem that can't be solved by fixed lines: When a player is fouled, he's awarded a free kick from whatever spot on the field the foul occurred. The opposing team is allowed to assemble a defensive wall of players at a distance of ten yards from the kicker. The problem is that people cheat. The ref sets both the spot of the free kick and the site of the wall, and as soon as he's not looking, the two may surreptitiously creep towards each other to improve their chances.
Which is why for this year's World Cup, you'll see the referees carrying an aerosol can filled with a white foamy substance, and they'll spray this on the pitch to clearly mark visual boundaries for the both the kicker and the wall. Seconds later the line mysteriously disappers. (Hardcore footie fans have already seen this spray as it's been in action for years, but this is the first World Cup where it's been used.) So what is this stuff, shaving cream?
Nope. This "vanishing spray" is called 9.15 Fair Play, patented by an Argentinean journalist named Pablo C. Silva. Silva was playing footie in a local league and had a crucial free kick of his blocked by a defensive wall--one that had rushed him to close the distance to a mere three meters. "The referee didn't book anyone and didn't do anything," Silva fumed to The Independent. "We lost the game, and driving home later with a mixture of anger and bitterness, I thought that we must invent something to stop this."
Silva came up with a mixture of water, butane and a surfactant compressed inside an aerosol can, and the foamy spray it emits is clearly visible, and disappears from view less than a minute after being sprayed. This had apparently been proposed as early as the '80s in other countries by other inventors, but it is Silva's patented product that the World Cup refs are now wearing in holsters. That is the best possible advertising in the world: FIFA claims that nearly one billion people watched at least some part of 2010's World Cup. We're guessing Silva's journalism days are probably over.
As for the name, "9.15" stands for 9.15 meters, which is equivalent to ten yards, the proper distance a defensive wall is supposed to remain from the free kicker.