Having won the Premier League eight times as a full-back, Gary Neville gives an insight into how the position has changed over time, from serving others to being key man.
To be a full-back today is a lot more difficult than 20 years ago, and probably 20 years before that too, for a number of reasons.
The changes in the rules of the game make it difficult. If you think about our treatment of Jose Antonio Reyes here with Arsenal in 2004, we were able to be really aggressive against him, put him off his game and stop him in his tracks. Today, I'd have been sent off. If a full-back treated a winger like that, he'd be sent off. But the change in rules is right.
Secondly, I think that wide players are not wingers any more. There are some wingers left, but if you look at the performances of Salah, Mane, Sterling, Bernardo Silva, they're scoring 15-20 goals a season. They're goalscorers. They're wide forwards who make the most difficult runs five, six, seven, eight times a half.
I used to have a guy outside me who would very rarely make a run inside me, who would wait for the ball to come to his feet, he'd try to get crosses into the box as part of a 4-4-2 system.
It changed a bit towards the end of my time with Manchester United, where I would say the game changed more, and I would say we had a lot more of what would be described as innovative players, who played in pockets or in-behind you.
But generally, the first 10 years of my career, I'd be playing against players like a Jason Wilcox, a really good winger who could cross the ball, or for instance Trevor Sinclair, a right-footed left-winger who would test you in a different way but generally would still be outside out you, very rarely inside you.
Or against Harry Kewell at Leeds, who again would play outside of you and try to put crosses into the box. These are the types of players I played against.
The modern full-back
Neville explains how the game has moved away from a flat back four, remembers the specific instructions he was given as a full-back in the 1990s, and why he himself would struggle in that position nowadays...
If I played now as a full-back against the types of players we've now got in the game, I would find it a lot more difficult. The speed of them is absolutely incredible now.
We talk about the modern full-back needing to be attacker, but I actually think it is a lot more difficult for them to defend. They also have to be better on the ball. They also have to be able to run 12, 13km a game. The demands on the modern full-back now are far greater than during my time.
It is wrong of me to sit here like the old full-back I am and say: 'In my day I could have done this or that.' It's far more tough for these lads.
I've got Brian Kidd's words ringing in my ear… "Support from behind, support from the back!" Away from home, first half an hour, we'd support from behind. Pass the ball and serve. I was like a servant at right back! Then you'd start to overlap. That was the first five or six years of my career.
I remember Steve Bruce and David May always pulling me in towards him, then all of a sudden Jaap Stam and Ronny Johnsen came, much more mobile as defenders, and that's where we felt the change. European defenders, comfortable defending in the wide area, which allowed me to go forward a lot more.
I think Roberto Carlos and Cafu changed the dynamic of how full-backs were viewed.
Klopp deserves credit
Though Liverpool's front men take the limelight, full-backs Trent Alexander-Arnold and Andrew Robertson are among the most-improved players in the league. Neville notes how academy graduate Alexander-Arnold and £10m signing Robertson are the epitomy of Klopp's influence at Anfield...
Liverpool's full-backs have to go down the line, because Liverpool's forwards work quite narrow, so if they weren't there, it would actually show. They have to be there.
Robertson has become a brilliant full-back. I have to say, defensively with England, we actually exploited him up at Celtic Park. We said: 'Make runs inside him, he'll be good going forward, but defensively you'll catch him.' What he's done at Liverpool has shocked me in terms of his defensive work.
We talk about Jurgen Klopp improving players. His work with Robertson and some of the other players - [Sadio] Mane, [Mohamed] Salah and [Roberto] Firmino in particular - these three are a complete different level now, and it's the same for Robertson. It's a brilliant performance from Jurgen Klopp.
Pep's demands incredible
City's full-backs are often seen level with the central midfield, and 20 yards ahead of their central defenders, something Neville says is one of Guardiola's most notable traits...
The first time I saw this was in Munich, against Man Utd in the Champions League quarter-final in 2014, and Pep's full-backs went into central midfield. I was thinking: 'What are they doing? I'd never seen anything like it in my life.
He's continued it with City. The demands that Pep puts on his full-backs is incredible. Pep's full-backs are also the main players alongside Fernandinho to stop the counter attack, so they always have to be in positions to ensure the attack is sustained, that they are available, and also that they form the shield across the back to stop opponents breaking out.
United's full-back issue
Since Sir Alex Ferguson left Old Trafford in 2013, Neville notes how United have struggled to find a suitable out-and-out full-back. Though Ashley Young and Antonio Valencia have been deployed there, Neville feels United should have spent bigger on a No 1 target, rather than trying several at a lower price...
I thought when I left that Rafael Da Silva was perfect as a Manchester United full-back. He was tenacious, aggressive, decent on the ball, and he was sold. Maybe rightly so, I'm not sure.
Ashley Young is not the person to start criticising at Manchester United; he's been asked to play right back, left back, left wing back, right wing back. He's doing it brilliantly well, but he's not a right back! I think Antonio Valencia did well for two seasons but I think he was more of a right winger.
I don't know why United have had such problems at right-back. You can't keep signing full-backs for £15m. Over the past few years they've spent nearly £100m on five full-backs.
City spent big on Kyle Walker, Danilo and Benjamin Mendy. Maybe United would be better buying the correct full-back first time up for £40m or £50m and have them for seven years, because it's cost them that much in the end trying different full-backs!
Sky Sports' Premier League games this weekend
Everton vs Burnley: Live on Sky Sports Premier League and Sky Sports Main Event Saturday from 7pm; Kick-off is 8pm
Bournemouth vs Tottenham Hotspur: Live on Sky Sports Premier League and Sky Sports Main Event Saturday from 12pm. Kick-off is 12.30pm
Newcastle vs Liverpool: Live on Sky Sports Premier League from 7pm and Main Event Saturday from 7.30pm. Kick-off is 7.45pm
Huddersfield Town vs Manchester United: Live on Sky Sports Premier League from 1pm and Main Event Sunday from 1.30pm. Kick-off is 12.30pm.
Arsenal vs Brighton & Hove Albion: Live on Sky Sports Premier League and Sky Sports Main Event Sunday from 4.15pm. Kick-off is 4.30pm.
Manchester City vs Leicester City : Live on Sky Sports Premier League and Main Event Monday from 7pm. Kick-off is 8pm.