Andy Robertson – Best Left-Back in the Premier League

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I must confess that I was amongst those potentially frustrated when Liverpool decided not to spend big money on a left-back last summer, instead plumping for Hull’s Andy Robertson. However, once I did some digging on Robbo, as I have several friends who support Hull, the overwhelming response was that it was a very positive signing and one who would be good value for money.

Nevertheless, I think it’s fair to say that Robertson has, pound for pound, probably been Liverpool’s best value signing under Klopp, and probably one of their best value for money signings in the PL era. For just £8m, which is a pittance in today’s market, Liverpool have picked up someone who is just 22 PL starts last season, has established himself as one of the best, if not the best left-backs in the Premier League.

What’s interesting about Robertson is that he’s not necessarily considered one of Liverpool’s key players. He’s not considered as important as VvD, or Salah, or Mane. But he’s playing in an important position, particularly given how Klopp has used the full-backs to introduce width to his team, and he’s been consistently one of Liverpool’s best performers – not just this season but since before Christmas.

I’m here to argue that he is, in fact, the best left-back in the league.

But before we look at any other Premier League left-backs, I want to look at the impact that Robertson has had on Liverpool, which means, inevitably, comparing him with Alberto Moreno.

In terms of overall impact on the team, Robertson has had a much more positive one than Moreno.

In Robbo’s 22 league games in 17/18, Liverpool recorded 14 wins at a 63.6% win percentage, securing 2.14 points per game. That’s the joint best win percentage in the squad (Robbo and Matip have the exact same record) and a points-per-game bettered only by Gini Wijnaldum (2.15). In terms of all competitions, only Oxlade-Chamberlain has a better win ratio (63.6%) than Robbo’s 63.3%, as the Reds won 19 of the 30 games he started.

In comparison, Moreno’s win percentage is one of the worst in the squad, down at just 42.86% in the Premier League, as the Reds won just six of the 14 games he started and just 11 of the 24 games in all competitions (45.8%). Moreno’s points per game in the Premier League is down at 1.71, 0.43 points per game lower than Robbo.

In terms of goals scored and conceded, the numbers reinforce that. Liverpool scored 54 goals at 2.45 goals per game when Robbo started, compared to just 28 in the 14 Moreno did at 2.00. And defensively the gap is even bigger, as the Reds conceded just 18 goals in Robbo’s 22 starts (0.82 per game) and 19 in Moreno’s 14 (1.36), over half a goal a game more. The net goal difference is 1.64 when Robbo was on the pitch, compared with 0.64 with Moreno on the pitch.

(N.B: there were two PL games where neither player featured, Liverpool’s 2-1 win over Burnley and their 0-0 draw with Everton).

And the underlying xG numbers indicate that Robbo has had a positive but marginal improvement to the attack. Liverpool’s average xG was 2.14 in games where Robbo started, compared to 1.90 without him (and 1.99 when Moreno was on the pitch, indicating Liverpool outperformed their xG with Robbo on the pitch and didn’t when Moreno was).

But the defence is where Robertson seems to have made the biggest difference – or at least was part of the improvement to the defence. Again, Liverpool conceded more xGA in Moreno’s 14 games than in Robertson’s 22. With Robbo on the pitch, the Reds conceded just 0.76xGA per game last season, compared to 1.19 without him (and 1.24 with Moreno in that position). So the Reds conceding a goal every two games less with Robertson instead of Moreno is backed up in the underlying numbers.

This, of course, has carried on into this season, as Liverpool’s Premier League xGA with Robbo in the team has continued to dip to 0.73, and goals conceded is now 19 in 26 games, also 0.73. So luck hasn’t played a seismic part in that.

One factor that is important to this is consistency. In games where Robertson has featured, Liverpool have conceded more than 1.0 xGA on just four occasions and more than 2.0 xGA on just one (Spurs at home).

On three of those occasions, the Reds have conceded penalties (worth 0.76 xGA apiece). In those four games, Liverpool’s open play xGA is 1.15 (Palace away), 1.13 (Arsenal away), 1.02 (Spurs at home) and 0.90 (Brighton away). Robertson, it has to be noted, was at fault for none of those four conceded penalties.

Now one thing that has to be noted is that other factors are important beyond Robertson’s addition to the team – the arrival of Van Dijk, Karius getting regular game-time etc. but nevertheless, Robertson’s promotion to first-team regular coincides with Liverpool’s xGA falling off a cliff, and I for one don’t think that that’s a complete coincidence.

Defensively, Robertson’s numbers stack up with the rest of the PL’s top six LBs. He made zero defensive errors last year, was dribbled past only 0.6 times per 90 minutes, with a successful tackle percentage of 70%. Compare that to Ashley Young, who was dribbled once per game, with a tackle percentage of 67%, Ben Davies who was dribbled 0.8 times per game with a 64% tackle percentage and Marcus Alonso, who was similarly dribbled 0.6 times per game with a slightly better tackle percentage 0.71%. But all three made one defensive error apiece.

Of course, many of the PL’s left-backs have been utilised as wing-backs, and Robertson is to an extent, no exception. Whilst he’s made a remarkable effect on Liverpool’s defence, and defensive stats, in general, are hard to quantify, what cannot be denied is that he was the most creative left-back in the division last season.

Last season, Robbo made 23 key passes at 1.06 per 90, but his xA was a hugely impressive 0.22 per 90. Compared to fellow LBs Alonso (0.10 xA/90), Young (0.14 xA/90) and Davies (0.14 xA/90), Robertson stacks up impressively, with only six full-backs creating more chances than him per game last season, and none of them with a higher expected assists.

The most impressive thing about Robbo’s creative numbers is the quality of chance he produces. With 4.77 xA created from 23 key passes, Robertson creates roughly 0.21 xA per key pass. That’s the highest in the Liverpool squad, and higher than anyone who created at least 0.3 xA/90. For context, the likes of KDB (0.12), Eriksen (0.13), Ozil (0.11) and David Silva (0.15) don’t get close. What it means is that whilst Robertson didn’t necessarily get the volume of created chances, what he did create was generally of a high quality – and he had a contextually high percentage of big chances created (a staggering eight big chances, more than a third of his total 23).

Whilst no expected assists per key pass or big chance per key pass ratio currently exists to check the entire Premier League against, I’d wager that there is almost nobody with a decent sample size that comes close to Robertson in this area.

What’s interesting is that Robertson seems to be keeping that ratio high this season, whilst also creating slightly more. Albeit from only four games, Robbo has created ten chances, 1.71 expected goals (0.43 xA/90 and 0.17 xA/KP), two big chances and two assists already. So we can see that there’s no doubt he’s picked up where he’s left off, and that is hopefully something we can see progress even further over the season.

Robertson’s main rival for the best left-back slot in the league has emerged this season in the form of Benjamin Mendy. Marcus Alonso scores more goals than any left-back, but creatively he’s not in Robertson’s league and defensively he has benefitted from a Chelsea system that was both inherently defensive and freed him up to attack. This season, we can already see that Arsenal have exposed Alonso’s channel, and he still has questions to answer in a defensive sense.

The same questions potentially hover over Mendy, who has exploded out of the traps. and last season, Mendy had an xA/90 of 0.24, higher than Robertson, but in a sample size of only 357 minutes and only four starts.

So it remains to be seen whether Mendy, who has played on the left-hand side of Manchester City’s midfield at times rather than their defence, can both sustain this level of attacking output and contribute defensively. The former seems likely given that Man City have been the best attacking side in the division for the last year and a bit, but the latter is where questions remain, as Mendy has been dribbled past more historically than Robertson, albeit he makes more tackles.

Overall, however, I would argue that right now, Andy Robertson is not only one of the best left-backs in the league, if not the best, but I would argue he’s one of Liverpool’s best players, most important players, and definitely one of their most underrated players. As Robertson himself says, nobody wants the left-back’s shirt. But maybe they should.

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