Dermot Gallagher returns with the latest Ref Watch and says Southampton should have been awarded a penalty against Aston Villa for a Matty Cash handball.
Southampton 0-1 Aston Villa
INCIDENT: Early in the game, Stuart Armstrong's shot hit Matty Cash on the arm inside the area. However, when looked at by VAR referee Mike Dean, he judged that the ball had hit Cash on the thigh before his arm and a penalty was not given.
DERMOT'S VERDICT: Incorrect decision.
DERMOT SAYS: "My immediate reaction was penalty. VAR looks at it and they are of the opinion it flicks off the thigh. The law is quite interesting in so much as it says if the ball rebounds off your own body and up to your arm, you can't give handball but there is a caveat that says if your arms are outstretched and in an unnatural position, you can still give handball.
"I think the best solution for me would be to give handball because the arm is outstretched. There are many others in the camp saying it has definitely struck his body so if it hadn't had flicked his thigh, it wouldn't have hit his arm. But, without doubt, his arm has stopped that ball progressing forward.
"The law is a bit complex and it depends on which referee it comes down to. As I say, I would have given a penalty. VAR on that day decided that part of the law and the ball striking his thigh allowed him not to."
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INCIDENT: In the final minutes of the game, Danny Ings had an equaliser ruled out for offside. Once again, VAR looked at the decision and showed that the bottom of his shirt sleeve was offside, meaning the goal remained disallowed.
DERMOT'S VERDICT: Decision made on fine margin.
DERMOT SAYS: "Can the lines be 100 per cent accurate? As I said earlier in the season, what you've got to accept is that all 20 of the stake holders bought into the system. It was the best system available.
"It was tried, tested, worked out and everybody bought into it.
"At the very start, people said VAR would be a fluid process in so much that we would have to tweak it over the years. It's transitional and we've seen things like this - we saw one earlier in the season with Patrick Bamford - but when they put the lines across, which is all they can do on that day, the line was just through to the bottom of his sleeve and as he can score with that part of his body, as we've seen earlier in the season, it's then disallowed.
"What I would say, it's the finest of margins and people would not have believed two years ago when assistants were making decisions like this, how tight the margins were.
"Now, everybody is seeing and saying: 'Wow, we didn't anticipate that'."
Arsenal 0-0 Man Utd
INCIDENT: Bruno Fernandes escaped punishment for a challenge on Granit Xhaka. He caught the Arsenal midfielder in the back of the shins with his studs up, but did not receive a booking.
DERMOT'S VERDICT: Should have been a yellow card.
DERMOT SAYS: "He should have had a yellow card. If you look, it's almost a stepping motion. He doesn't come along way, he doesn't come at great speed and that's what stops it from being a red card.
"It's not nice, there's no doubt about that. It is reckless, but I don't think it is endangering the safety of an opponent. If you don't come along way, you don't gather that speed and if you don't gather that speed you don't have the intensity."
Dermot: Let's hope we do not need concussion subs
Starting from Saturday, the Premier League will allow teams to use concussion substitutes.
Teams participating in the Premier League, FA Cup, Women's Super League and Women's Championship will be able to permanently substitute players who are diagnosed with, or suspected of sustaining, a concussion during a match.
Both sides in each game will have two such replacements available, as well as their three regular substitutions.
Speaking on Ref Watch, Gallagher added: "The simple thing of it is we hope and pray that it never has to be used. Nobody wants to see that situation, but we do have a care and a duty of attention to players, and over the last couple of years we've seen some bad head injuries.
"If this does occur on Saturday or going forward, we now have that caveat. It's there to be used and it's a bit like insurance. You have to buy it, but you hope it never has to be used."
The lunchtime game between Aston Villa and Arsenal on Saturday will be the first Premier League fixture under the new regulations.