Argentina approves vanishing spray
The spray has been used on an experimental basis in the second division for the last six months and the Argentina Football Association (AFA) has now approved its use in the top flight, officials said on Wednesday.
Referees pace the regulatory 9.15 metres between the ball and the nearest defender and then spray a white line on the pitch to mark the correct position of the wall.
The line then disappears from the pitch within a minute.
Referees carry the spray in a small aerosol can weighing 115 grams.
Pablo Silva, a sports journalist who invented the spray and has worked with chemical engineers to develop the product, said the idea came to him when he was foiled at a free kick during an amateur game several years ago.
"In the 88th minute, we were losing 1-0 and won a free kick on the edge of the area. When I took the kick, the wall was three metres away," he told Reuters earlier this year.
"The referee didn't book anyone and didn't do anything.
"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."
A spray has been used in some competitions in Brazil in the last few years for the same purpose. Silva said the products were different and had been developed separately.