During the 2014 World Cup, referees have been using a disappearing spray to mark lines for players to stay behind before free kicks. Some of the more intense fans have found their own use for it.
Dedicated World Cup fans have started using the spray to keep people away when they're trying to watch the games. You can see a picture of the new use for the spray below.
I wonder if anybody gets a yellow card for trying to step across the line while the game is on.