It is the debate which seemed to have been settled a few years ago – is the modern full-back really a defender any more, or is he closer to a winger?
Pep Guardiola's Barcelona really changed the game, with Dani Alves often operating so high and wide on the pitch that he was part of the attacking unit. Manchester City have followed that trend.
Liverpool have earned plaudits for years under Jurgen Klopp for how their defenders push up the pitch, not least Trent Alexander-Arnold. The 21-year-old has emerged as a brilliant provider of assists and can cross the ball like David Beckham in his prime.
Gone, seemingly, were the days of wide defenders simply being cloggers. The conversation seemed to be over. All hail the flying full-back.
And yet, in another part of the north west, a new point is being made in the discussion.
Aaron Wan-Bissaka, like Alexander-Arnold, is part of a glut of talented right-backs that have emerged in England in recent years.
He broke through at Crystal Palace under Roy Hodgson, looking solid beyond his years, and earned a £50million move to Manchester United in the summer.
Unlike Alexander-Arnold, though, his game is all about defending. Over the weekend, Rio Ferdinand said: 'If you moulded them two players together, Aaron Wan-Bissaka and Trent Alexander-Arnold, you've got the best player.
'Aaron Wan-Bissaka one-versus-one, I've seen [Raheem] Sterling play against him and Sterling rinses everybody, he finds it hard against Wan-Bissaka.
'One-versus-one he will match you physically, he will run with you, he will slide on the floor if you're getting away from him a little bit more and he has to go into overdrive.
'He can cover people, unbelievable. He could play right side of a back three at Man United if they wanted to, I think he'd be brilliant there.'
He also acknowledged Wan-Bissaka's flaws compared to Alexander-Arnold: 'On the ball nowhere near as good as Trent, but Trent defensively one-on-one isn't anywhere near as good as Wan-Bissaka, so if you had both of them you've got the ultimate machine.
'It depends on the game. If I knew I was going to have to defend a lot and I need someone to lock down the winger I'm bringing Wan-Bissaka on.'
Ferdinand hit the nail on the head when it comes to the pair. You will likely not see a pair of players operating at the elite level in the same position who have as disparate styles of play.
The stats back his point up too. Alexander-Arnold has 12 assists to his name in the Premier League this season, while Wan-Bissaka has two. The United man has no goals, compared to Alexander-Arnold's two.
Go deeper into the stats going forward and the difference becomes even clearer. Liverpool have seen 75 chances provided by Alexander-Arnold – the most in the Premier League for a defender – while Wan-Bissaka has provided just 20 for his team-mates.
Admittedly, only 40 of Alexander-Arnold's are from open play – he is also a set-piece specialist – but that's still a huge gap.
Wan-Bissaka has attempted less than half the number of crosses Alexander-Arnold has put in – at 75 compared to 195 – which says a lot about the Liverpool man's positioning.
And while Alexander-Arnold has managed 48 touches in the opposition box, putting him 10th in the division for defenders, Wan-Bissaka does not crack the top 10.
On the other hand, Wan-Bissaka hugely outperforms Alexander-Arnold in defensive metrics.
The 22-year-old has managed 99 tackles in the Premier League this season, putting him second for defenders behind just Ricardo Pereira. Meanwhile, Alexander-Arnold has attempted just 45 tackles.
Guardiola once famously said he did not coach tackles, and it is fair to say that the sliding challenge has gone out of the game to a degree.
Positioning and organisation is just as important.
But what is a small issue is that Alexander-Arnold has consistently been dribbled past more by opponents than Wan-Bissaka.
He has suffered that fate 40 times this season, compared to Wan-Bissaka's 19.
It allows Wan-Bissaka to completely mark the likes of Raheem Sterling out of games, while Alexander-Arnold sometimes gets dropped in favour of more solid options for big matches.
Wan-Bissaka has also won more duels, at 175 to Alexander-Arnold's 60.
What is clear is that Ferdinand was right. As it is, these are two brilliant full-backs with one sizeable flaw in their game. If you were to mesh them together, you'd have an all-time great player in the position.
The real test will be seeing who England go for in the future. It will be a symbolic choice, a decision between solidity and creativity.
At the least, the debate is now back on. What is a modern full-back? When it comes to Alexander-Arnold and Wan-Bissaka, two different answers have emerged.
Source: m.allfootballapp.com