The introduction of video assistant referees was one of the major issues heading into this World Cup and, as expected, it has been a near constant talking point during the first round of games. But FIFA says it is "extremely satisfied with the level of refereeing to date and the successful implementation of the VAR system". David Elleray, technical director of the International Football Association Board - the body which oversees the laws of the game, told BBC Sport its overall impact has been very positive. "There have only been five reviews in the first 17 matches, which conforms to the global average of one in every three games," said Elleray, who helps to train referees in the use of VAR. "This is 'minimal interference' and with the outcome of three matches being directly affected by the VAR intervention this is 'maximum benefit' and a fairer World Cup. The behaviour of players has been excellent, with only one red card and a low average of yellow cards and little mobbing of referees." Here, we take a look at the incidents so far and get Elleray's verdict on whether VAR worked in each case.
England – Tunisia
The first incident in the Group G game in Volgograd came in the 39th minute. Ferjani Sassi, who had scored a debatable penalty four minutes earlier for Tunisia, appeared to grab Kane in the penalty area and wrestle him to the floor from an England free-kick. The video assistant referee, Sandro Ricci of Brazil, did initiate a review but no penalty was awarded. The second incident, at an England corner in the 52nd minute, appeared to show Kane being pulled to the floor by Yassine Meriah. Again the decision was checked, again the same outcome.
Elleray: "The incident in the first half is more blatant than in the second half. FIFA said referees would be strong on clear holding in the penalty area, so it is not clear why the VAR did not recommend an on-field review, unless he felt that there were also offences by other England players."
France – Australia
In the 54th minute of France's Group C game against Australia in Kazan, France forward Antoine Griezmann was challenged by Josh Risdon. Referee Andres Cunha waved play on but, after play continued for about 20 seconds, he stopped the game and headed to the review screen by the dugouts, before awarding the penalty. Griezmann converted to set France on their way to a win.
Elleray: "The initial challenge by the Australia defender looks fair but close examination shows that the defender then lifts his leg to trip Griezmann. This is something the referee did not see and thus he made a clear error in not awarding a penalty kick. Correct VAR intervention."
Brazil – Switzerland
Brazil were leading their Group E opener with Switzerland when they felt defender Miranda was pushed as Steven Zuber headed in a 50th-minute equaliser. The Brazilians also felt Gabriel Jesus was manhandled inside the Switzerland penalty area later in the second half, but neither incident appeared to be reviewed by VAR.
Elleray: "Brazilian anger is retrospective; there is no immediate reaction from the Brazilian defenders when the goal is scored. There is always some pushing and shoving in the penalty area and the referee's decision not to penalise the attacker is not a clear and obvious error."
Peru – Denmark
With the Group C game between Peru and Denmark goalless in the 44th minute in Saransk, Christian Cueva went down in the area under a challenge from Yussuf Poulsen. Referee Bakary Gassama waved play on but, again, after play continued for about 23 seconds, the official blew his whistle and stopped play to consult the review screen. A penalty was awarded to Peru, but Cueva couldn't cash in, shooting over.
Elleray: "This is a clear referee error and the VAR intervention allows fairness to prevail and the correct decision to be given, which directly affected the final result. VAR at its best."
Sweden – Korea
Sweden's Group F game with South Korea appeared to be drifting towards a goalless draw in Nizhny Novgorod when Viktor Claesson fell under a Kim Min-woo challenge in the Korean penalty area in the 65th minute. Referee Joel Aguilar initially allowed play to go but called a halt moments later. He looked at the incident again on the pitch-side screen and about 90 seconds later Andreas Granqvist scored the penalty that was awarded.
Elleray: "This is a very clear missed penalty and it is somewhat surprising that the referee made such a clear error. This incident shows how VAR has brought greater fairness to the World Cup as this penalty directly affected the result of the match."
Russia – Egypt
In Group A match between Egypt and Russia, Mohamed Salah was held by Roman Zobnin when running into the area. The holding began outside but continued into the 18-yard box. Initially referee Enrique Caceres gave a free-kick but VAR deemed the infringement was inside the box.
Elleray: "The laws of the game clearly state that if holding starts outside the penalty area and continues into the penalty area it is a penalty kick. This was a good example of the VAR assisting the referee to make the correct decision."