Pierluigi Collina has urged football identities to lay off Serie A's refs.

"The job of a referee has changed a lot and we must always keep learning. Our work is never done, especially as it is impossible to achieve perfection," said the refereeing designator.

"I should note that we never spoke of 'zero tolerance' and on television there are often confusing or just plain incorrect messages sent to the fans.

"If a player makes contact with the ball, that does not mean it isn't a foul. There is no rule stating an accidental collision causing a player to fall is a foul.

"As for shirt-tugging, the rules speak clearly that you cannot grab hold of an opponent. The referee does well to penalise a shirt-tugging incident.

"It is difficult to get uniformity in the decisions, as everyone sees an incident with their own eyes, but we are working on using a common language, so all referees can receive the same instructions."