A few years ago, FIFA advised referees that they needed to be within 10 or 15 yards of the action rather than running the diagonal. Now the trend has been even further refined, with a referee needing to know exactly what angle he needs to be at to get the clearest view of a challenge.

"It's one of the most difficult things in the world to spot. If you're not in exactly the right position then it's almost impossible to tell whether it's a foul or a dive," Shield said. "You give a foul and then later on you look at a replay and you see you've been fooled."

FIFA has instructed referees to award yellow cards for cheating at this year's tournament in an effort to cut it out.

FIFA president Sepp Blatter said in Munich that referees were better prepared for this tournament than they had ever been before.

"There are more people there with the referees to prepare them and to test them than there are referees, and they have been tested at all levels," Blatter said. "We can't do more for the referees. I trust the referees. We'll have a good World Cup.

"Of course, referees are human beings and human beings make sometimes make errors ¡ª we have to accept that. They will be very careful in acting as referees ¡ª I have confidence in the way they've been prepared."

Blatter said he had delivered only one message to referees: Stop players from elbowing each other.

"I gave them only one instruction, to protect the good games and to protect the good players and to pay special attention to the devil that has come into our game: elbowing," Blatter said.

He said it occurred when players were jumping for headers and did not keep their arms at their sides.