FIFA are set to implement VAR (video assistant refereeing) for the first time at a World Cup this summer in Russia after it has already been rolled out in multiple professional leagues, including the Bundesliga, Serie A and Major League Soccer.
Some think the introduction of VAR at the highest level of football is something that has been long overdue, while others claim that its use is too premature – with the potential to disrupt the flow of the game.
Regardless of views, VAR is to be used at the sport's showcase event this summer in Russia, and Goal takes a look at all the details of how it will work, as well its regulations – including retrospective punishment.
How will VAR work at the World Cup?
Instances of using the VAR are pretty straightforward, and will be used in similar fashion as in the Bundesliga and MLS. Referees in Russia will be able to consult the VAR for help on four sorts of decisions: goals, penalty decisions, direct red cards and cases of mistaken identity.
Regulations state that the referee must always be the one to make the decision and that decision will stand until it is "clearly wrong". The referee will only be able to view, on video, the start of the phase that has led to the incident, and a goal scored through a throw-in which should have gone to the other team will not be disallowed under the new VAR system.
Furthermore, if the ball is still in play, the referee must wait until it is in a neutral zone before stopping all course of action. The play will then restart with a drop ball if the decision is not overturned.
One example in a World Cup final where VAR might have overturned a missed call was in the round of 16 fixture at the 2002 World Cup in South Korea and Japan between the United States and Germany. With Germany leading 1-0 in the second half, USMNT defender Gregg Berhalter stuck a shot that beat Germany goalkeeper Oliver Kahn but struck midfielder Torsten Frings hand on the goal line.
Had a handball been called, it would have been a red card for Frings with the USMNT receiving a penalty for a chance to level the scoreline. Instead, no call was made and Germany went on to hold on for the 1-0, and an eventual trip to that year's final.
While the referee of that match claimed he did not think it was a deliberate handball in real time, former Premier League referee Howard Webb, who also refereed the 2010 World Cup final, told Sports Illustrated in 2017 the correct outcome of the play should have been a red card and penalty kick.
What are some VAR concerns?
There has been a fair amount of criticism about the introduction of VAR at the World Cup, with some stating that referees constantly checking the video assistant would disrupt play and, at times, the process can be a very delayed. Fans, coaches and spectators attending the matches are also left in the dark when the referee is checking the VAR.
Tottenham manager Mauricio Pochettino criticised the use of the VAR in the Carabao Cup and FA Cup fixtures this past season, denoting his fears about how the use of technology would kill the emotion and ethos of the game.
"It is a game of emotion. If we are going to kill this emotion I think we are going to change the game," he told reporters.
"It's difficult for the referee - I feel so sorry for the referee and more I feel sorry for the fans because it's so difficult to understand the situation."
Additionally, UEFA president Aleksander Ceferin said that VAR will not be used in next season's Champions League.
"Nobody knows exactly how VAR will work. There is already a lot of confusion," said Ceferin.
"I am not at all against it but we must better explain when it will be used. We will see at the World Cup."
How will retrospective action work?
Referees in Russia will be allowed to give out red cards for off-the-ball incidents through VAR. This means that players can be sent off if incidents are picked up on by monitors.
IFAB (International Football Association Board) technical director David Elleray stated: "If there is something away from the action that has been missed and it later comes to the attention of the VAR or the assistant VAR, then they can inform the referee and he can send the player off, even if it is later in the match.
"We do not anticipate this happening very often... this would only be for serious red-card offences."
The World Cup will start on June 14.