World Cup video assistant referees (VARs): What you need to know

There will be many firsts in the 2018 World Cup but perhaps the biggest is the introduction of the video assistant referee. Whether you like it, loathe it or are indifferent to it, VAR is part of football's future and, for the first time, it is part of the global game.

Trials of VAR around the world in various leagues have produced mixed results: some injustices have been corrected, some interminable waits have been suffered and some shambolic farces have been endured.

It seems a bold move to use a system still in its infancy at the World Cup but ever since trialling it at the Confederations Cup last summer, FIFA have seemed dead set on using VAR in Russia. Will it be a success? Will it be a disaster? Will we notice?

What is VAR?

We'll give you the short version: VAR is a system used to correct "match-changing" decisions that may have been missed or incorrectly judged by the on-field officials. Those "match-changing" scenarios are, as defined by FIFA: goals and offences leading up to a goal, penalties and offences leading up to a penalty, straight red card incidents and instances of mistaken identity.

How will it work?

At the World Cup, referees will be in contact with the VAR hub in Moscow, which will be checking for "clear and obvious" errors in every game. For subjective decisions -- fouls, handballs and so on -- they will then advise the referee if they believe an incident is worth looking at again on a pitch-side monitor. In that instance, the referee will draw a square with their hands to indicate a review will take place.

Objective calls, like whether the ball has crossed a line, will be dealt with by the technology. Offside decisions also fall into that category despite a degree of subjectivity inevitably being part of some decisions.

The VAR team will have access to 33 cameras at each ground, dotted around crucial parts of the pitch, some of which will be ultra slow-motion. This is all in addition to goal-line technology, which will also be in use, as it was at the last World Cup in Brazil.

Where has VAR been used?

Italy and Germany have been the two most prominent European leagues to use VAR, introducing it last summer and for the whole 2017-18 season, as well as Portugal. In England, it was used on a trial basis in selected FA Cup games. Similarly in France, it was trialled in some French League Cup games, and it's also been in place in Major League Soccer since August 2017. Yet the A-League in Australia were the real pioneers, being the first to use it in a competitive match back in April 2017. Clubs in Brazil voted against its introduction while the J-League in Japan will be introducing it next year.

What improvements have been suggested for the World Cup?

One of the key weaknesses of VAR as it has been used to this point is the uncertainty it causes inside the stadium. Fans may not see the referee make the requisite signals, without any form of announcement over the PA or on a big screen they might not know what is being reviewed, and they ultimately might not know why a decision has been overturned. However, FIFA have promised to keep fans more reliably informed by updating the progress of any review on the big screens in each ground. Someone in the VAR hub will have a tablet from which they will relay messages to broadcasters, and the people actually at the games.

FIFA said: "The person operating the tablet is located in the video operation room and has access to the audio from the referee communication system as well as the camera angles the VAR is looking at. The VAR information system will also be used to automatically create VAR-specific graphic templates for TV and the giant screen in the stadium."

When VAR has worked...

VAR was first used in England for the FA Cup tie between Brighton and Crystal Palace in which a Brighton goal, scored by Glenn Murray, was confirmed by the technology. Even the opposing manager, Roy Hodgson, was pleased with how the system was implemented. "The referee was helped by the fact he had [Neil] Swarbrick in the VAR studio making a judgement that'd help him out -- so I have no complaints," said Hodgson.

The first significant use of VAR in England came in the FA Cup match between Leicester and Fleetwood Town, when Kelechi Iheanacho's strike was initially ruled out by the on-pitch officials for offside only for the video officials to reinstate it. In that situation, the process was relatively quick and ultimately produced the correct outcome.

In Serie A, Cagliari were awarded a penalty on the opening day of the season against Juventus, the video officials spotting that Alex Sandro had fouled Duje Cop. In Germany, RB Leipzig's Timo Werner was initially given a penalty in a game against Hamburg only for VAR to spot that the defender who challenged him had actually won the ball cleanly.

These are a just a few examples of decisions that have been correctly overturned, and you can probably count the many minor calls that have been verified among its successes too.

When VAR has not worked...

You could probably say that when VAR is good, it's very good but when it's bad, it's horrid. A few recent, high-profile examples of the problems and confusion with VAR include the A-League Grand Final between Newcastle Jets and Melbourne Victory, when the only goal of the game was quite clearly offside, but a few moments earlier, the system used by the VAR officials malfunctioned. TV coverage showed that an obvious error had been made but because the official technology was faulty, it could not be corrected.

Lawrie McKinna, CEO of the Jets (who lost the final), wanted the match replayed. "That was the first thing I asked," he said, but to no avail. "We understand the disappointment and frustration of the Newcastle Jets," said A-League chief Greg O'Rourke.

Then there was a Bundesliga game in March, when Mainz and Freiburg players were heading for the dressing rooms at half-time, only to be brought back on when VAR awarded a penalty, which was duly scored. There was high farce in Portugal when a flag blocked the camera, meaning an incorrect offside decision could not be corrected.

Perhaps the most egregious error so far came when Vancouver Whitecaps defender Kendall Waston was sent off early in their MLS game against Atlanta United, after a five-minute delay while VAR was consulted. Waston had collided with Atlanta defender Leandro Gonzalez Pirez with his arms slightly raised, so it was determined that he was guilty of violent conduct and thus dismissed.

"My blood was boiling," said Whitecaps head coach Carl Robinson. Vancouver went on to lose 4-1 only for the sending off to be overturned a few days later. Though VAR ultimately led to the correct decision, it wasn't of much use to the Whitecaps.

Who will be operating VAR?

FIFA announced their list of 36 referees and 63 assistants in March. Some of those officials have experience using VAR, such as Iran's Alireza Faghani, who refereed at the Confederations Cup, Gianluca Rocchi, the Italian referee who is an enthusiastic advocate of it and American pair Mark Geiger and Jair Marrufo, who have used it in MLS.

But many of the officials will have no practical experience of VAR, which is why they have been and will be put through their paces in a series of refereeing camps before the tournament. Some of those on the FIFA list will only be on-pitch officials, whereas some will be in the VAR hub in Moscow.