Calls for the use of technology in football have been loud for years, particularly using video replays to judge whether a ball has crossed the line. But the most successful innovation at the World Cup in Brazil is a simple can of foam.
If you've been watching the World Cup, you may have spotted the referees drawing lines on the field with a mysterious white foam.
Innovation: Cameroon's players stand behind a line marked by a free-kick marker spray. Photo: AFP
The explanation gets more mysterious – the foam vanishes in about a minute.
But the reason why referees have started wielding cans of the stuff will surprise no football fanatic.
It is used to keep the opposition their required 10 yards away from a player taking a free kick. This distance is frequently encroached upon by restless players wanting to get back into play.
Ivorian referee Noumandiez Desire Doue uses his spray in the Socceroos' game with Chile. Photo: AFP
"It's a vital tool for ensuring that the rule is observed," English referee Howard Webb told The New York Times.
Created by journalist Pablo Silva in Argentina, the foam has been popular in the region since 2008.
It was used for the first time in the opening game between Brazil and Croatia.
But the foam is not the only new technology debuting at the World Cup this year. Above each of the stadiums are 14 new cameras trained on the goal line.
But rather than wait for a video referee or two to watch the footage back and make the best decision they can with the footage angles they've got, the footage picked up by the camera is processed by software.
Very quickly after the potential goal may have been scored, the result will buzz on a specially built watch the referees are wearing.
Both innovations have been warmly received, particularly the goal line after a debacle at the 2010 World Cup where referees denied England a goal against the Germans when it hit the crossbar and bounced into the goal, despite video evidence showing it clearly should have been a point.
FIFA's president at the time, Sepp Blatter, apologised to the English team and viewers for the error. "It is obvious that after the experiences so far at this World Cup it would be a nonsense not to reopen the file on goal-line technology," Mr Blatter said.
"We will naturally take on board the discussion on technology and have the first opportunity in July at the business meeting."
All 12 stadiums in Brazil have had the German technology installed. It has also been installed in stadiums in Germany, Britain and the Netherlands.