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Marcos Alonso is one of the most attacking full-backs in world football, but has his role changed since Maurizio Sarri joined Chelsea?

Ever since the Spaniard joined the Blues, he has been given license to get forward and join attacks at every opportunity. Alonso was originally granted this freedom by former boss Antonio Conte, who used him as a left wing-back, in a formation operating with three centre-backs. This meant that Alonso didn’t have to focus on his defensive duties as much, given that he had enough cover behind him.

However, when Sarri joined Chelsea, many people asked the question as to whether Alonso would be able to handle a more defensive role, in the new bosses 4-3-3 set up. Well, when you look at the Blues’ results so far, it can’t be going that badly, can it? Not yet, anyway. But is Sarri really playing Alonso at left-back, or is he allowing him to carry on operating at left wing-back? Let’s take a look.

Alonso’s position on the field

Below you will see the heat maps from Alonso’s appearances last season in the Premier League, compared to this campaign.

Marcos Alonso Chelsea Tactical Analysis Statistics
Alonso’s heat map 2017/18 Premier League season
Marcos Alonso Chelsea Tactical Analysis Statistics
Alonso’s heat map so far this season

As you can see, the heat maps are incredibly similar, despite the fact that Alonso is supposedly now operating as a left-back. Just like last season, the Spaniard is featuring more in the opponent’s half than he is his own, which shows that he is still attacking just as much as he was under Conte. What else is quite notable, is that Alonso quite rarely enters his own box to defend which, if he was playing as an out and out left-back, then the heat map would reflect that and show him popping up in there more often.

What do the stats say?

Now let’s take a look at some stats from Alonso playing at left wing-back last season and compare them to his appearances this season, to see if there is much difference between the two – given that he is now supposed to be playing more of a defensive role.

First up, how Alonso compares defensively this season.

Marcos Alonso Chelsea Tactical Analysis Statistics
Alonso’s defensive stats 17/18 Premier League season
Marcos Alonso Chelsea Tactical Analysis Statistics
Alonso’s defensive stats so far this season

Just like the heat map, Alonso’s defensive contribution has not been too dissimilar so far during this campaign. However, as you would expect with less defensive cover, his stats have increased slightly. The defender is winning more defensive duels on the floor and in the air – but he is down on interceptions – which is a key part of his game.

Interestingly, Alonso is making more recoveries in the oppositions half than he was last season, which means he must still be playing quite high up the pitch if his numbers have increased in that avenue. But a few key defensive attributes appear to have improved for the full-back, though, as he is now blocking more shots, making far more clearances and committing fewer fouls.

Now for the offensive numbers – a huge part of his game last season, of course.

Marcos Alonso Chelsea Tactical Analysis Statistics
Alonso’s offensive stats 2017/18 Premier League season
Marcos Alonso Chelsea Tactical Analysis Statistics
Alonso’s offensive stats so far this season

On the whole, remarkably, Alonso’s offensive contribution has been elevated this season. Although we are only a few games into the campaign, the full-back is averaging almost as many goals and his assists have shot up considerably. He is taking more shots and making more crosses per game, even if his accuracy percentages have tumbled. Alonso loves to face up against the opposing right-back and take them on, and it seems as though he is doing that more regularly, with over a 9% success increase.

The defender is now winning a higher percentage of his duels, taking more touches a game in the opponent’s box and is making more progressive runs, as he looks to go beyond the midfielders in front of him on a regular basis. So, has his offensive role really changed much? These stats suggest not.

Offensive and defensive positional sense

As previously mentioned, Alonso was allowed to play higher up the pitch last season, at the risk of being caught out as he had more defensive cover behind him. Seen as though he is now operating in a back four, you would expect his position to have changed into more of a deeper defensive role.

The graphic below suggests otherwise.

Marcos Alonso Chelsea Tactical Analysis Statistics

In this instance, Alonso pushed up far too high on the winger that he was marking. As the ball was played into his man, Alonso was caught too square which allowed the Cardiff player to pop the ball off to a teammate. The defender then went through his man who you can see laid on the floor and Alonso was left in no man’s land. Fortunately for the Blues, Jorginho quickly covered round and delayed the Bluebirds’ full-back from progressing further forward.

Yes, it didn’t come to anything in the end, but this is what happens when a left-back is allowed to push too far forward – which Alonso will not stop doing until he is told otherwise. Better teams will exploit this weakness.

Now let’s take a look at a graphic that supports the argument further that Alonso is still operating predominantly as a left wing-back under Sarri.

Marcos Alonso Chelsea Tactical Analysis Statistics

Time and time again, Alonso has been getting into positions such as this. With Chelsea pushing forward, the Spaniard makes a progressive run well beyond the highlighted Eden Hazard and even Olivier Giroud, to become the furthest player forward. On-loan Real Madrid man Mateo Kovačić looks up and sees Alonso’s run and tries to pick him out with a ball in behind the Cardiff defence, which the Blues’ number 3 just doesn’t quite latch onto.

Let’s face it, left-backs do not get into positions such as this on a regular basis, especially when they are playing in a back four. Again, if this was a better team than the Bluebirds, then they could have sprung a quick counter-attack down Chelsea’s left in Alonso’s absence. Arsenal actually did on a couple of occasions last month. It really is a dangerous tactic to employ and, perhaps it is an unnecessary risk, given the attacking prowess the Blues already have within their ranks.


Alonso is certainly still being granted an awful lot of offensive freedom, even in Sarri’s 4-3-3 formation. The left-backs numbers have increased on both ends of the field, though – so for now – it seems to be working for Chelsea. But as has been previously mentioned a couple of times, better teams will eventually figure this tactic out and will look to exploit the Blues down their left-hand side. Until then though, you can expect to see Marcos Alonso continue galloping forward for Sarri’s side.