VAR in the Premier League: How did first weekend go for technology in top flight?
VAR has arrived in the Premier League and, as expected, it is already dividing opinion.
After a quiet debut in England's top flight on Friday, with no high-profile reviews required in Liverpool's opening-day win over Norwich, it took centre stage over the weekend.
The Premier League has spent two years monitoring its use in a host of other competitions, including major European leagues, the Women's World Cup, the Champions League and the FA Cup - and has developed its own set of guidelines for how it will be used.
To help with its implementation, the league embarked on a summer educational programme, running sessions with players, managers and the media to ensure everyone knew what to expect.
So, as VAR played a part in the top flight for the first time in England, did it run smoothly and, crucially, did it get the important decisions right?
Was VAR's first weekend outing a success overall?
After all the testing - including operating VAR dry runs on live games - this was the first occasion where the VAR team at Stockley Park have had to deal with four matches at one time.
"After two years of training everyone has been really excited to get started with VAR," said Chris Foy, the former Premier League referee who is part of the team overseeing the implementation of VAR. "Did it go well? As Raheem Sterling said after the Manchester City game, if we're getting the decisions right then it can only be a good thing."
One of the major concerns with VAR has been how it transforms the experience for fans at games. The Premier League has acknowledged this and taken steps to ensure communication is clear at the grounds.
Messaging flashes up on big screens and, in the event of an overturned decision, 18 of the stadiums (not Anfield or Old Trafford) will display a definitive clip clarifying the reason for the VAR intervention.
"There were certainly positive and negatives about it inside the stadium," reports Gary Rose, who was covering Manchester City's 5-0 win against West Ham at London Stadium for BBC Sport, where VAR was a prominent part of the match.
"Its addition undoubtedly added to the drama and atmosphere in the stands, with the decision to rule out Gabriel Jesus's second 'goal' buoying the West Ham fans and initiating a spell of gallows humour as both sets of fans chanted 'VAR, VAR, VAR' for any slight incident in the game.
"On screen the graphics to show a VAR review was taking place and the subsequent decision were clear, as were the accompanying announcements over the speakers.
"However, a penalty incident which saw Sergio Aguero's spot-kick saved and then scored after a retake did lead to confusion in the stands, with both sets of fans unsure why it was being retaken.
"By the end, I found myself checking the screen every time there was a potential flash point. It's debatable whether fans would find that a welcome addition to the VAR-era Premier League."
Former England captain Alan Shearer was happy with what he saw. "The way it is being used is very different to what we've seen in the Champions League and the Women's World Cup," he said on Match of the Day. "They are using a high bar for VAR involvement and if it stays like that then it should be a success."
The Premier League said about 70 incidents had been checked and former referee Dermot Gallagher was happy with how the system has worked. He said: "I think it's a great platform and a great start. We've seen three decisions overturned and all three could not have been clear with the naked eye.
"It will get better, they will get faster and it will become more commonplace. People will grow into it and it's been a really good start.
"I wish I had it when I was a referee. I can look back at a few mistakes I made. As a referee, why would you not want to have it?
"It's new, everyone has to embrace it. There are people that do not believe in it but people will say it's the best thing that has happened in football."
The weekend's key incidents
West Ham 0-5 Manchester City
Seven checks in total, two overturned decisions
The incident: Early in the second half and with Manchester City 2-0 up, Raheem Sterling plays the ball across for Gabriel Jesus to tap in. As the Brazil forward celebrates, a message appears on the big screen to signal a VAR review is in progress. The goal is ruled out because Sterling's shoulder is offside. The definitive clip is played on the big screen.
Former England captain Alan Shearer on BBC Radio 5 Live: "The law within the Premier League is that you are either offside or you're not so you can't really argue it. The technology has improved, it's not going to be 100% accurate but it is going to be consistent."
Manchester City manager Pep Guardiola: "You have to be mentally strong when VAR is not on your side. You think at 0-3 the game is almost over but at 0-2, the game is completely different. You have to be calm and be strong. It is going to change the dynamic, not just for the team but for the spectators."
Former England midfielder Joe Cole on BT Sport: "An important thing happened. When the Manchester City goal was disallowed that would have been 3-0, it galvanised the stadium. There was an emotional response and it lifted West Ham, albeit only for about three minutes! That was interesting - that lift of being on the good side of the decisions - and how that evolves is one to keep an eye on."
Foy's verdict: "All goals are checked as a matter of routine. In this case it is a factual decision - in the build-up to the goal you can clearly see Sterling is offside so it is a straightforward decision to overturn the goal."
The incident: Sergio Aguero's late penalty is saved by Lukasz Fabianski. But the VAR checks the incident and West Ham midfielder Declan Rice is penalised for encroachment, although some people suspect the award is because West Ham's keeper has moved too early off his line. Aguero steps up again and this time makes no mistake to put City 4-0 up.
Former England defender Paul Parker on BBC Radio London: "It's disillusioning fans, this whole process, at this moment in time. We're not going to be talking about games of football any more or individual players. We're going to be talking about, I don't know what to call it... maybe a dictator?"
Ex-England defender Rio Ferdinand on BT Sport: "If you add too much to this game you are going to detach it from the everyday man or woman coming in to the game. Look at American sports - a lot of people outside America wouldn't watch it because they think there's too much going on and too many rules. That's the beauty of our game - it's simple, everyone can play it. That's starting to change now and I hope it doesn't go too far."
Foy's verdict: "What we're looking for with encroachment is what we call 'direct impact'. Because it was Rice who encroached and Rice who cleared the ball, the decision was a retake."
Burnley 3-0 Southampton
Six checks in total, no overturned decisions
The incident: Ashley Barnes squares the ball to Chris Wood following a slip by Jack Stephens and Wood taps in. The whistle goes immediately to disallow the goal as the assistant's flag is up. The VAR takes a look just to check. As suspected by everyone in the ground, the on-field decision stands - no goal.
Foy's verdict: "The referee blew his whistle once the ball went it because the assistant had flagged. If there is a clear offside the assistant will flag as they always have done and the advice is for the referee to allow the play to continue, which is what happened here."
The incident: Che Adams catches Ben Mee with his follow-through early in the first half. Referee Graham Scott awards a free-kick but no further punishment. The VAR agrees - no red card and the game continues.
Foy's verdict: "The bar is set high - the VAR will only overturn a 'clear and obvious' error. This did not fit that criteria."
The incident: Another red card review. This time Burnley's Johann Berg Gudmundsson clatters into Southampton's Ryan Bertrand. A free-kick - but no card - is the on-field decision. After a VAR check, that verdict stands.
Foy's verdict: "To overturn a decision, we are looking for the kind of incident where everyone goes 'crikey'. This wasn't one of those."
Watford 0-3 Brighton
Six checks, no overturned decisions
The incident: Roberto Pereyra smashes a second-half Watford free-kick into the wall. He runs straight up to referee Craig Pawson shouting for a handball but the referee is not having it. VAR agrees in double-quick time.
Foy's verdict: "This is an interesting one because you have to consider the new laws on handball. What we are looking for is whether the player made themselves unnaturally bigger. In this case, Glenn Murray hadn't so it didn't fit the criteria to change the decision."
Bournemouth 1-1 Sheffield United
Six checks, no overturned decisions
The incident: Bournemouth defender Adam Smith is booked for a late challenge on Sheffield United's Jack O'Connell. VAR checks to see whether a red card should be given - but agrees with the on-field decision and Smith's caution stands.
Former Sheffield United midfielder Michael Brown on BBC Radio 5 Live: "Adam Smith was just trying to put pressure on, the yellow card was the right decision, it was never a red."
Foy's verdict: "A straightforward one - no 'clear and obvious' error."
The incident: Bournemouth attack and the ball falls to Philip Billing via Joshua King. Billing's superb shot from 25 yards brings a diving save from Blades keeper Dean Henderson. There is a pause as VAR checks for a foul on King in the build-up but nothing is given.
Foy's verdict: "This was just to make sure there had been no foul in the build-up. There was certainly no significant interference, so no need for VAR to intervene."
The incident: Sheffield United's John Fleck is booked for a jumping challenge on Jefferson Lerma. Referee Kevin Friend gives a yellow and, for the third time in the game, VAR supports the on-field official's decision.
Foy's verdict: "It's important to note the referee will be talking with his assistants all the time so will be taking in their views when making a decision. This will have been one such case and they got it right."
Tottenham 3-1 Aston Villa
Seven checks, no overturned decisions
The incident: John McGinn goes down in the Tottenham box as Danny Rose races in to stop him shooting. Chris Kavanagh says no penalty and VAR agrees.
Former Premier League referee Dermot Gallagher's verdict: "McGinn just pushed the ball a bit too far in front of him and then barged into Rose. No penalty."
The incident: McGinn is involved again. Kyle Walker-Peters is furious after he thinks he gets a boot on the floor from the Villa midfielder, but a quick VAR check says no red card.
Gallagher's verdict: "This was a check just to make sure nothing untoward had happened. It was a tangle between the players but no red card offence."
Leicester 0-0 Wolves
One overturned decision
The incident: Early in the second half Leander Dendoncker thinks he has broken the deadlock when he finishes from close range after his first header hit Wolves team-mate Willy Boly following from a corner. However, the review shows that the ball struck Boly's arm from Dendoncker's initial header.
Gallagher's verdict: "It was only controversial as people were not aware the law had changed. It was correct - the referee has no choice. The law changed in the summer and if a player is struck on the arm or hand by the ball and it goes into the net then the goal will be disallowed. It is a mandatory thing, there's no grey area."
On Wolves' boss Nuno Espirito Santo's complaints that the decision took too long (one minute 38 seconds), Gallagher replied: "When we were watching they wanted to be right and we had to look at different angles to make sure it had hit his arm, not his head, and you would rather take a few seconds to get it right."
Manchester United 4-0 Chelsea
Checks for each of the goals and the penalty, no overturned decision
The incident: Marcus Rashford goes down in the box following a rash tackle from Kurt Zouma. Referee Anthony Taylor rules that the Chelsea defender caught the forward and VAR backs him up following an efficient review and a penalty is confirmed.
Gallagher's verdict: "Absolutely the right decision - it was a foul and Zouma took down Rashford. But there was a brilliant advantage from the referee as Jorginho fouled Andreas Pereira on the way through."
There were six checks and no overturned decisions in Crystal Palace's 0-0 draw with Everton on Saturday, but none were for high-profile incidents. On Sunday, Arsenal's 1-0 win at Newcastle included a check for the goal with no overturned decisions.