Video Assistant Referee causes controversy every week in the Premier League, but how are decisions made, and are they correct?
After each weekend we take a look at the major incidents, to examine and explain the process both in terms of VAR protocol and the Laws of the Game.
In this week's VAR Review: Was the red card for Ipswich Town's Leif Davis against Arsenal the correct decision, and should Newcastle United's Fabian Schär have been sent off after bringing down Aston Villa striker Ollie Watkins?
Plus incidents involving Liverpool, Manchester United, Manchester City and the other major talking points.
Ipswich 0-4 Arsenal
Possible red card overturn: Davis challenge on Saka
What happened: Leif Davis attempted to make a tackle on Bukayo Saka in the 32nd minute, but was late and caught the Arsenal player on the Achilles. Referee Chris Kavanagh immediately produced the red card, which was checked by the VAR, Darren England. (Watch here)
VAR decision: Red card stands.
VAR review: Premier League referees have come in for criticism this season for failing to identify and punish serious foul play, but perhaps this is the kind of situation which shows at least some lessons have been learned.
In November, Leicester City midfielder Wilfred Ndidi escaped a red card when he challenged Chelsea's Cole Palmer.from behind, not getting close to the ball and placing his studs into his Achilles. The Key Match Incidents (KMI) Panel ruled that it should have been been a red card on the field, but felt it didn't reach the threshold for a VAR intervention.
However, referees' chief Howard Webb later said that he would expect a red card to be shown because the foul was on a "vulnerable part" of the body, endangering the safety of an opponent. Webb said: "We've looked at this collectively, among the officials, talked about this, and we would prefer this to be dealt with with a red card. We have to protect player safety."
There's no doubt other challenges may have appeared as bad as Davis', but there's a crucial difference when a player has no prospect being able to play the ball. In this case, Saka had already released a pass when Davis stood on him, which suggests the only intention was to foul the opponent. Intent is no long within the wording of the laws, but it can indicate malice.
Verdict: The missed red card for Everton defender James Tarkowski against Liverpool showed there's still a lot of improvement needed when it comes to serious foul play decisions.
Ipswich may say that there wasn't a high degree of force involved, but this kind of challenge has a high chance of causing injury to an opponent.
If the referee had only shown a yellow card, it should have been upgraded to a red through VAR with clear evidence of force, as Saka's ankle buckled.
Aston Villa 4-1 Newcastle
Possible red card: DOGSO by Schär
What happened: Ollie Watkins attempted to run onto a long ball in the 13th minute, but was hauled down by Fabian Schär. Referee Jarred Gillett produced a yellow card for stopping a promising attack while the VAR, Michael Salisbury, checked if it should be upgraded to a red for denying an obvious goal-scoring opportunity (DOGSO).
VAR decision: No red card.
VAR review: There's a common misconception that DOGSO is purely about being fouled by the "last man," but it's actually an assessment about the quality of the goal-scoring chance that would have ensued. It's possible to get a red card with another defender ahead of where the foul took place, all that matters is how the attacker has been affected.
There have only been two VAR red cards for DOGSO this season, and both went to Arsenal players: William Saliba at AFC Bournemouth, and Myles Lewis-Skelly against West Ham United. In addition, the KMI Panel found there was a missed red card for Villa's Ian Maatsen after he brought down Crystal Palace's Ismaïla Sarr.
Every DOGSO situation is unique, though we can use elements of the three previous incidents to show why a caution for Schär was an acceptable outcome.
With the Saliba red card -- which, coincidentally, Gillett was also on VAR duty for -- Evanilson was brought down a long way from goal but the ball was coming to a stop in the centre of the field, not running through to goalkeeper David Raya, who was backtracking. Lewis-Skelly had similarities as his foul happened on the halfway line; Mohammed Kudus would have gained control of the ball with Raya a long way out of his goal, which would have provided an immediate scoring chance.
On the missed Maatsen intervention, Sarr was in a central position with the ball running forward into the area. The VAR, Alex Chilowicz, backed the yellow card on the field, but this should have been upgraded.
The VAR's main question for the Watkins chance was the likelihood of gaining and keeping possession, and then being able to take a shot. When fouled by Schär, Watkins was under the flight of the ball, and it then bounced through to Newcastle United goalkeeper Nick Pope. You couldn't say with certainty that Watkins would have been able to take control of the long pass, rather than it simply running through to Pope. With Saliba, Lewis-Skelly and Maatsen, there was no doubt that the attacker would take the ball well before any opponent and have the chance to shoot.
Verdict: You could call this a possible scoring chance, rather than an obvious one. If the pass to Watkins had dropped closer to the striker, or if it had been played along the ground, the VAR may have had a bigger decision to make, because there would be a greater probability of the striker taking control of the ball.
Possible penalty: Schär challenge on Watkins
What happened: Watkins picked up a pass from Morgan Rogers in the 27th minute and looked to move past Schär, going down and asking the referee for a spot kick.
VAR decision: No penalty.
VAR review: Schär placed his leg across to make a challenge, but didn't make direct contact with Watkins. The Aston Villa striker then clipped the calf of Schär and went down.
Verdict: This would be a soft penalty, but there's a case for it as Watkins didn't move into the Newcastle defender to initiate the foul.
However, it's the kind of penalty that would have to be given on-field, which would then be supported by VAR as Schär did make a challenge and there was contact. We wouldn't expect the VAR to intervene if it's not given.
Brentford 4-2 Brighton
Possible red card overturn: Violent conduct by Pedro
What happened: João Pedro was sent off in the 61st minute when the Brighton & Hove Albion striker appeared to throw his arm into the face of Nathan Collins. Referee Tim Robinson produced the red card, which was checked by the VAR, James Bell.
VAR decision: Red card stands.
VAR review: When these two teams met in December, Pedro escaped without a red card after throwing an elbow toward Yehor Yarmoliuk. That was a clear VAR error, with the VAR, Chris Kavanagh, failing to send the referee to the monitor; it's logged as one of the 12 missed interventions so far this season.
This time, Bell was only required to confirm the decision of the referee.
Verdict: This should have been Pedro's second red card of the season, remarkably for the same offence against the same opponents.
That said, if the referee hadn't given the red card himself you wonder if this one would have gone to review -- simply because the cameras did not present the best replays and there didn't appear to be any close ups. You could see something had probably happened -- there might have been a kick out too -- but it probably needed the referee to give it.
Possible penalty: Flekken challenge on Welbeck
What happened: Brighton were on the attack in the 16th minute when Brentford goalkeeper Mark Flekken made a hash of an attempted clearance. Danny Welbeck moved onto the loose ball, and eventually went ground under pressure from the goalkeeper. Referee Robinson ignored appeals for a penalty, and it was checked by the VAR. (Watch here)
VAR decision: No penalty.
VAR review: Flekken had come to try to claim the ball, but it was Welbeck who got a touch first.
However, rather than being brought down by Flekken, it looked as though the Brighton striker moved his body into the goalkeeper to ensure there was contact.
Verdict: Welbeck's unnatural movement meant there was never likely to be a VAR review. A striker is within their rights to accept contact and win a penalty, but they can't initiate it themselves.
Possible penalty: Challenge by Henry on Dunk
What happened: The game was in the 84th minute as Brighton pushed forward looking for an equaliser. Yasin Ayari played a corner into the area, and after Jan Paul van Hecke had got his head to the ball it looped up, with Lewis Dunk going down under pressure from Rico Henry. Brighton wanted a penalty, and it was checked by the VAR.
VAR decision: No penalty.
VAR review: As the ball was in the air, Dunk and Henry both had hold of each other. It's unclear if the Brighton player went to ground as a result of Henry's actions or if he actually pulled the Brentford player down with him.
Verdict: If two players are involved in mutual holding, which was the case in the initial stages of the incident, there won't be a VAR intervention for a penalty.
Leicester 0-1 Liverpool
Possible goal: No foul by Daka on Alisson
What happened: Leicester City thought they had taken the lead in the 66th minute when Wilfred Ndidi's shot ballooned up, Patson Daka muscled Liverpool goalkeeper Alisson Becker off the ball and played a short pass to Conor Coady to head home from close range. However, as soon as the ball crossed the line, referee Stuart Attwell blew for a foul by Daka. As he held the whistle until the ball crossed the line, that allowed the VAR, Michael Salisbury, to check it.
VAR decision: No goal.
VAR review: Goalkeepers are often accused of getting too much protection, but they also have to be judged slightly differently as they have the right to collect the ball with their hands. If an attacker does something which prevents them from being able to do that, a foul is always likely to be the outcome.
Daka has a look to see where Alisson is, before knocking him off the pitch as he's about to play the ball. If this had happened with two outfield players then it's unlikely to be seen as a foul, but this was a goalkeeper being prevented from playing the ball by an opponent whose only intention was to stop him doing so.
Verdict: Once the referee has given this on the field, there's no prospect of a VAR intervention.
Man United 0-1 Wolves
Possible penalty: Bentley challenge on Mount
What happened: Christian Eriksen played a ball into the area with the outside of his right foot, which was angled to Mason Mount. The Manchester United substitute put his shot well wide, but was caught afterwards by onrushing goalkeeper Daniel Bentley as he looked to make a block. Referee Rob Jones allowed play to continue, but was there a case for a penalty? (Watch here)
VAR decision: No penalty.
VAR review: While there was contact by the goalkeeper on Mount after the ball had gone, it looked to be a simple consequence of two players going for the ball, rather that Bentley committing a foul.
In such cases where both players have a right to make a challenge, the VAR is looking for a reckless challenge to make an intervention.
Verdict: Two weeks ago, Fulham felt they should have been awarded a penalty when Liverpool goalkeeper Caoimhín Kelleher collided with Andreas Pereira. The VAR in that game, Matt Donohue, decided it was a natural coming together as the goalkeeper tried to smoother the ball. But the KMI Panel voted 4-1 that it was an on-field and VAR error; there should have been an intervention for a spot kick because the contact was "significant."
Perhaps if Fulham hadn't won the game 3-2, that incident might have been more high profile.
Donohue was on VAR duty for this Man United game too, but the Bentley incident won't go down as a missed intervention.
Everton 0-2 Man City
Possible penalty: Harrison challenge on Savinho
What happened: Savinho tried to get on the end of a Kevin De Bruyne cross in the 13th minute, but went to ground under pressure from Jack Harrison. The Manchester City player appealed for a penalty, but referee Simon Hooper wasn't interested.
VAR decision: No penalty.
VAR review: It's difficult to see if there was any contact by Harrison on Savinho. Perhaps the Everton player had an arm on his back, but it was no more than that.
Verdict: Savinho went down far too easily, under little pressure, for this to reach the threshold for a VAR review.
Possible penalty: Handball by Savinho
What happened: The game was in the 42nd minute when Harrison received the ball inside the area at the back post. He tried to play a pass across the box, but the ball hit Savinho. Everton fans appealed for penalty, though the players weren't interested and neither was referee Hooper. The VAR, Darren England, checked it.
VAR decision: No penalty.
VAR review: The ball was hit at Savinho from close range and it deflected off his tight and on to his arm, which was in an expected position.
Verdict: There have only been eight handball penalties in the Premier League this season and in those cases it was for a deliberate act, or the arm being fully extended away from the body. There was no chance of this going to a VAR review.
Some factual parts of this article include information provided by the Premier League and PGMOL.