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: Should Diogo Jota and Oliver Skipp have both been shown red cards in Liverpool vs. Tottenham? Was Richarlison denied a penalty? And what about spot-kick claims in matches involving Manchester City and Manchester United?
Possible red card: Jota challenge on Skipp
What happened: In the 81st minute, the ball bounced up just outside the centre circle and as Oliver Skipp went to head it he was caught on the side of the head by the studs of Diogo Jota, who was attempting to nick the ball away with a raised foot. The challenge drew blood and referee Paul Tierney produced a yellow card for Jota, but should it have been a red?
VAR decision: No red card.
VAR review: Jota is fortunate. This should probably be a red card, but that doesn't necessarily mean it's an incorrect decision for the VAR, David Coote, not to intervene -- such is the nature of VAR.
While there is a strong case that Jota endangered the safety of an opponent, at the same time it could be argued that Jota was only reckless -- which is a yellow-card offence. Does Skipp put his head into the area where Jota is playing the ball, rather than the Liverpool player directly kicking his opponent? Did Jota try to play the ball and not expect Skipp to attempt the header? They are all questions the VAR must ask.
In August, when Manchester City beat Crystal Palace 4-2 at the Etihad, Erling Haaland caught Joachim Andersen with his studs in the side of the head. Referee Darren England awarded the free kick but didn't even caution the Norway international; the VAR, Simon Hooper, decided it wasn't worthy of a red card. City were 2-0 down at the time and went on to win 4-2 with Haaland scoring a second-half hat trick.
Likewise, at Anfield it was Jota who went on to be the matchwinner in injury time, yet the Haaland situation didn't pick up the same attention. The Independent Key Match Incidents Panel ruled that the VAR was correct not to intervene and send Haaland off.
While there are similarities, perhaps in the Jota case his foot is slightly higher with his studs more flush to his opponent. Haaland was also less aware of the position of Andersen, who had moved from around the side. The Jota challenge has a stronger case for a red.
Compare it to Sadio Mane's challenge on Ederson in September 2017. The Liverpool striker was completely off the floor and jumping when he caught the Manchester City goalkeeper in the head with his studs, with force in the challenge. That is an example of a certain red card, while Jota isn't as clear cut.
It could be argued that attempting an overhead kick is far more dangerous than simply trying to get to the ball before an opponent, but such incidents are rarely punished with a red card. At the end of Aston Villa's 1-0 defeat at Manchester United, Calum Chambers kicked Luke Shaw in the head, and while he conceded a free kick, there was no card.
This is where the expectations of fans and pundits and the reality of VAR protocol collide. With a high threshold for intervention, it's not always a mistake for the VAR not to advise an overturn -- even if public opinion might say otherwise. The panel may well decide that while this wasn't a clear and obvious error for the VAR to get involved, the referee should have produced the red card. There is a growing list of this category of judgements, which suggests while VAR is improving there is still plenty of work for chief refereeing officer Howard Webb to do regarding decision-making by officials on the field.
Questions about the process would be cleared up by the VAR audio being played out after a match (FIFA forbids it being broadcast live in any games), and that's something Webb is working toward to improve transparency and help fans understand how and why decisions are made.
Possible red card: Skipp on Diaz
What happened: In the 33rd minute, Skipp challenged Luis Diaz on the edge of the area. While the Spurs player got a toe to the ball first, his follow through then caught the Liverpool forward above the ankle. Referee Tierney gave no decision and play continued.
VAR decision: No red card.
VAR review: Tierney obviously saw that Skipp won the ball but completely missed the follow-through contact, and should have awarded a free kick to Liverpool and showed the yellow card.
On a weekly basis we see similar tackles, where a player is stepping into a challenge, gets the timing slightly wrong and catches the opponent above the boot. It has been consistent throughout the season that these haven't been VAR red cards. To cross the threshold for intervention, the VAR is looking for a player coming in with force, leaving the ground or making contact from behind high above the boot.
Take Virgil van Dijk's challenge on Amadou Onana in September, when the Liverpool defender caught Onana higher on the shin after stepping into a challenge. Referee Anthony Taylor issued a yellow card, which wasn't upgraded after a VAR check.
If the referee gives a red card in these situations it won't be overturned, but they haven't been awarded through VAR.
If this challenge had happened a yard further forward on the penalty area line, then it could have been reviewed as a possible penalty, and then Skipp could have been booked. But the VAR is powerless simply to say a yellow card has been missed for a tackle outside the box.
Possible penalty: Konate on Richarlison
What happened: In the 85th minute, a cross came into the area from Pedro Porro. Ibrahima Konate had his left arm on Richarlison's chest and the striker went to ground asking for a penalty. Referee Tierney made it clear there was no spot kick.
VAR decision: No penalty.
VAR review: While Konate took a huge risk by having his arm across the chest of Richarlison, the Brazil international appeared to go to ground in a way that didn't fit with the level of contact. Richarlison seems to arch his back to imitate being pulled back. The Liverpool defender wasn't pulling or holding the shirt of Richarlison, so it wouldn't be considered a clear and obvious error not to give a penalty.
If the referee had awarded it, then it certainly would have stood -- as we'll see in the Palace vs. West Ham game.
Possible penalty overturn: Aguerd on Eze
What happened: In the 63rd minute, Eberechi Eze turned to move towards goal inside the area. West Ham United defender Nayef Aguerd held an arm out on the Crystal Palace forward, who went to ground. Referee Craig Pawson pointed to the penalty spot, but there was a VAR check.
VAR decision: Penalty stands, scored by Eze.
VAR review: This is the dichotomy of VAR protocol in all leagues. You can have the Richarlison penalty claim which isn't awarded and yet Aguerd's challenge on Eze, which has far less contact, isn't overturned.
If there's contact by the defender on the attacker, even if slight, then there should be no VAR intervention; a penalty should only be overturned if the defender gets a touch on the ball (and the challenge isn't reckless), or there is no contact, or if the contact is initiated by the attacker.
Even though this penalty is extremely soft, there's little chance the VAR, Jarred Gillett, would intervene to cancel the penalty.
Possible penalty: Chambers on Rashford
What happened: In the 72nd minute, Marcus Rashford had the ball in the corner of the penalty area and went to ground under a challenge from Calum Chambers. Referee Jarred Gillett ignored the penalty claims.
VAR decision: No penalty.
VAR review: While there was contact between the Aston Villa defender and Rashford, there was certainly nowhere near enough for a VAR penalty to be awarded. If anything, Rashford backs into Chambers rather than being fouled himself.
The contact on Rashford's right boot is minimal, and certainly not enough for the VAR to consider it has made the striker go to ground.
Possible penalty: Walker on De Cordova-Reid
What happened: In the 68th minute, Bobby De Cordova-Reid went to ground in the area in a challenge with Kyle Walker. Referee Simon Hooper wasn't interested in the penalty claims, much to the frustration of the Fulham player.
VAR decision: No penalty.
VAR review: A weaker claim than Richarlison against Liverpool, with De Cordova-Reid theatrically throwing himself to the ground. It's the Fulham player who seems to have his arm around Walker first if anything, and if there's holding taking place between both players there will be no spot kick.
Possible offside: Wissa on Dasilva goal
What happened: Brentford grabbed a dramatic winner in the 94th minute when Josh Dasilva scored from just inside the area, but there was an offside check against Yoane Wissa, who could have been in the line of vision of Nottingham Forest goalkeeper Keylor Navas, or impeding defender Ryan Yates.
VAR decision: Goal stands.
VAR review: There wasn't a subjective decision for the VAR to make, as the offside technology showed Wissa was onside. It was close, however, and the Brentford player needed the built-in tolerance level (lines touching.)
Forest were furious after the game, with boss Steve Cooper once again casting doubt about a decision without any real grounds. They questioned why there was only one line on the offside image, yet when the tolerance level is required for an onside decision only a single green line is shown to the defender, as had been the case for two seasons.
"I'm waiting to see the clear-cut image to make it OK. You can't make it on judgement or assumption," Cooper said. "If he is offside, he would have been affecting with the goalkeeper's vision. If it is onside, it is onside. I really hope at this stage of the game and the season that they didn't make a call when they're under pressure on assumption.
"I hope I see [an image where Wissa is definitely onside]. It's a massive call. It will make the headlines for you guys."
If Wissa had been offside, he could have been obstructing Navas' line of vision by moving towards the ball. Equally, it could be argued that his presence in front of Yates meant the Forest player was unable to make a play for the ball and prevent it getting through to goal.
Penalty overturn: Handball by Vina outside area
VAR decision: Penalty cancelled.
VAR review: You can see why the officials may have gotten this one wrong, as Vina was running towards the area and ended up inside the box.
But it was a quick and easy decision for the VAR, Craig Pawson. Vina was clearly outside the area when the ball struck his arm, so the penalty was overturned to a free kick on the edge of the area.
Information provided by the Premier League and PGMOL was used in this story.