TURIN (Reuters) - If the five referees system had been in use in 2005, former referee Pierluigi Collina would not have awarded the goal that gave Chelsea a Champions League round-of-16 win over Barcelona.
Chelsea were leading the second leg 3-2 but heading out of the competition on the away goals rule until they won a corner in the 76th minute.
Collina said he kept his eyes firmly fixed on John Terry, knowing that the other Chelsea players would do everything they could to allow their captain a free header.
Sure enough, when the ball was floated across, Terry got free of his marker and sent a low header into the bottom corner from around 16 metres. But Collina was so focussed on Terry that he did not see a foul by Chelsea defender Ricardo Carvalho on Barcelona goalkeeper Victor Valdes in the goalmouth.
"I was focussed on these two players (Terry and his marker) and I couldn't see what was going on in the goalmouth," Collina, now head of UEFA's refereeing body, told reporters on Tuesday as he showed a replay of the incident.
"My choice was correct because I predicted what had happened (that the ball would go to Terry). But the contribution of someone here (on the goal line) would have been very important and very easy, he would have been there, three metres away (from Carvalho). He could have informed me there was a foul."
The use of extra referees on each goal-line, officially known as Additional Assistant Referees (AAR), was pioneered by UEFA and approved by football's rule-making body, the International Football Association Board (IFAB), in 2012.
UEFA now uses it regularly in the Champions League, Europa League and European Championship and says that 35 member associations have also adopted the system to some extent.
"Some are using additional assistant referees in every match such as Turkey, Italy, Hungary and Belgium, others use the AAR system only in key matches or in one game per match day, or in the playoff or the last game of the national cup," Collina said.
He added that many people did not appreciate what the extra officials did, especially as they are not allowed under the laws of the game to use flags.
"Everyone knows they are there but very few understand their main purpose," he said. "Too often we hear comments saying that they are there for nothing, not deciding anything, that they are simply standing beside the goal. Very few can appreciate the contribution they make to the refereeing process."
Collina said that AARs could help a referee to judge whether the ball had crossed the goal-line and also give him an additional pair of eyes.
“They are not just an alternative to goal-line technology,” he said. "The referee shares the control (with the assistant), they can look at the same incident from two different angles," he said.
Collina showed one incident at a corner with two clusters of players in the penalty area, one in the goalmouth watched by the assistant and one on the edge of the area watched by the referee.
"With two people, they can focus on each area," he said. “One man on his own cannot see them. It’s almost impossible.”
"They can also act to deter players from committing fouls," he said, listing the benefits.
The only thing the assistants cannot do is wave a flag.
"They cannot flag but believe me, they are shouting in the microphone telling the referee what has to be decided," Collina said.
(Editing by Ed Osmond)