Much has been made of the impact and difference of Chelsea’s playing style since the arrival of Antonio Conte. Seeing that most of the squad that won the title in 2014-15 is on the current 2016-17 squad, this leads us to the question: “what is the difference between the two?” Specifically, how is the style between the two teams different?
With the new tools STATS has developed using machine learning, we can see where the teams are similar and where they are different. In this article, we run through a playing style “checklist,” which enables us to have a better understanding of how they have achieved success in these respective seasons. Overall, it will give us a sense whether there is a distinct change in playing style under Conte, whether they are the same – or somewhere in between.
Comparison No. 1: Creating and Executing Chances
The first thing to compare is how many chances each team created, and how effective they were in executing those chances (see Table 1 for summary). In the 14-15 season, Chelsea created around 15.1 shots per game, which is slightly above what they are achieving this year (14.6) but not significant.
What is staggering though, is how effective they have been in converting chances this year. The expected goals (xG) measure is a tool we can use which estimates the likelihood that the average league player will score a goal based on the situation (i.e., ball position, game-context etc. – see [1] for more details). This year, across 35 games, Chelsea have scored 75 goals but have an expected goal value of 54. Given that one of these goals were from two own-goals, their xG plus-minus (xGpm) is +19, meaning that Chelsea have scored +19 more goals this season than expected[1]. This compares to the 14-15 season, when Chelsea had a xGpm of +8.5 and scored 73 goals but were expected to score 63.5 (one of those was an own goal as well).
Table 1: Comparing the chance creating and execution between the 14-15 and 16-17 Chelsea squads.
In terms of explaining why Chelsea are more effective this season compared to the 14-15 version, let’s look at the individual contribution of the top scorers for the respective seasons (see Table 2). In the 14-15 season, Diego Costa was the leading goal scorer, netting 20 goals from an expected value of 14.8 – meaning he was +5.2 better than the average striker that year. The next-leading scorer was Edin Hazard, who scored 14 goals, with a plus-minus of +1.2.
Fast forward to this season, where Costa has been the leading scorer with 20 goals so far. However, his plus-minus has only been +2.4. Hazard has also been a leading light, scoring 15 but with a plus-minus of +4.5. Probably the key difference between this year and other years, has been the contribution of the other players – not in terms of the number of goals they have scored but by how efficient they have been. Pedro and Willian have been excellent – and in terms of their effectiveness in front of goal, they have been quite clinical with plus-minuses of +2.6 and +4.6, respectively. Even Marcos Alonso has been effective from his customary left-wing-back position, chiming in with six goals, with a plus-minus of +2.5.
A thought of Jose Mourinho teams in the past has been their reliance on individual brilliance instead of focusing on offensive team play. This table suggests that Conte has been able to extract more from other key offensive players – not just Costa and Hazard. This begs the question: Do Chelsea create chances in a different manner from Mourniho’s 14-15 team, or are they just better finishing the chances?
Table 2: Table comparing goals-scorers of the 14-15 season and the 16-17.
Comparison No. 2: Is there any difference in how they created chances?
Even though the 14-15 and 16-17 teams created approximately the same amount of chances per match, there could be a difference in how they created the chances. Recently, we have created a dictionary of scoring methods which are described below: Build-Up/Normal, Counter-Attack, Direct-Play, Corner Kick, Free-Kick, From-Free-Kick, Cross, From Cross, Throw-In and Penalties. In Figure 3, we show how many chances were created for each type of shot.
Figure 1: The creation of chances between the 14-15 and 16-17 seasons.
In Figure 3, we can see a number of things:
- In the 14-15 season, 50.1% of the chances created were in the build-up style, compared to this year, which is 37.7%.
- This season, Chelsea are creating more chances from direct-play, free-kicks and crosses.
- There is no difference in terms of chances created for counter-attacks, corner-kicks and penalties.
As Chelsea are +19 in terms of expected goals plus-minus, does this change where the goals are coming from? In Figure 4, we show the comparisons of how they’re scoring. The key points are that Chelsea are getting fewer goals from build-up and corner kicks and more from the counter-attack and direct-play in the 16-17 season.
Figure 2: Where are the goals coming from? Comparison of goals between the 14-15 and 16-17 squads.
Comparison No. 3: Conceding Chances
Now that we have compared the offensive performance between the 14-15 and 16-17 squads, we can do the same on the defensive side. Table 3 gives a summary of both teams. The first thing to notice is that the current squad gives up far fewer shots per game (8.6 vs 11.2). When we look at the expected goal plus-minus, we can see that Chelsea were -4.9, meaning that they should have conceded nearly five more goals then they have (see next comparison on goalkeeping to see a reason why this was the case). This season, their plus-minus is 1, meaning that they have conceded one more goal than what we would expect them to have.
Table 3: Comparing how opposition teams created and executed chances between the 14-15 and 16-17 squads.
A strong cue into describing the defensive discrepancy between the two seasons relates to goalkeeping. Using the expected save (xS) value, which estimates the likelihood that a goalkeeper should have saved a shot based on the game situation (i.e., player position, ball position and game-phase). In Table 4, we can see that Thibaut Courtois was more effective in the 14-15 season with a expected-save plus minus of +4.3 compared to this year’s -0.5. This means that he saved four goals more than the league-average keeper would have saved in the 14-15 season, compared to -0.5 goals this year – just below the league average.
Table 4: Comparing goalkeeping performance between the 14-15 and 16-17 squads.
Comparison No. 4: Playing Styles
Using a new metric, which we have developed at STATS, we can break up all continuous play possession into a series of “style” states, which automatically assigns a portion of a game into one of these distinct game phases. These style names are quite self-descriptive (i.e., direct-play, counter-attack, maintenance, build-up, sustained-threat, fast-tempo, crossing, high-press – but for more details see [2]).
In Figure 3, we compare Chelsea’s playing style. Generally, they have a similar possession percentage, and a similar amount of direct play. But there is a substantial relative increase in counter attack, from 14.2% to 24.5% compared to the league average. To give this increase some context, Leicester last season showed a +26.2% in counter attack, just slightly above Chelsea this year (and Leicester were considered very counterattack-heavy). Interestingly, Leicester paired that with an above average direct play, whereas Chelsea are well below average in this respect.
In terms of the possession-based styles (i.e., maintenance, build up and sustained threat), while they have a similar amount of possession, they seem to be less offensive when they have long possessions than they were in 14-15. In terms of the other style categories, there was a big increase in fast-tempo this season, which means they had more possessions where they circulate the ball quickly in the opposition’s half. In terms of crossing, this season they were on par with the league average in terms of crossing, whereas before they were quite a bit below the league average (+0.6% this season, -24.1% in 14-15). In terms of high pressing, they do less than in 14-15.
Figure 3: Chart comparing Chelsea’s playing style in 14-15 vs 16-17.
Summary: Chelsea Composite Squad: (Formation 3-4-3)
Based on our analysis and advanced metrics, we have put together a composite starting 11. As the 3-4-3 this year has been more effective defensively, we have used this formation.
Goalkeeper: Thibaut Courtois (14-15)
Back 3: Cesar Azipuleta, David Luis and Gary Cahill (c) (all from the 16-17 squad)
Left Wing-Back: Marcos Alonso (16-17) – due to his goal-scoring feats and as well as the defensive exploits in this 16-17 title winning squad).
Right Wing-Back: Pedro (16-17) – obviously being played out of position and Victor Moses would feel hard done by, but there were some other performances from the 14-15 squad that were impossible to not include.
Holding Midfielders: N’golo Kante, (16-17) and Nemanja Matic (14-15) – this year’s PFA player picks himself, but Matic’s imperious form in 14-15 was monumental in helping the Blues win the title.
Forward Three: Cesc Fabregas (14-15), Diego Costa (14-15) and Edin Hazard (16-17) – Fabregas was immense in the 14-15 season (and has played some very important cameos this season) and deserves a spot in the starting 11 (although he played out of position). Diego Costa has been a colossus in both seasons, scoring 20 goals in each – we choose the 14-15 season version as he was slightly more efficient in terms of xG. Similarly, both versions of Edin Hazard would be first name of the team-sheet, but again, due to his xG efficiency this season, the 16-17 version gets the starting birth.
Manager: Antonio Conte – both the 14-15 and 16-17 squads were similar in a lot of their attributes. But in terms of sheer efficiency in both offensive and defensive departments, Conte gets the nod by revamping the squad and by changing formations – which ultimately altered the fortunes of this Chelsea squad.
[1] In our analysis, we have classed own-goals down to luck, so in determining the “expected goals plus-minus” (xGpm) we exclude own goals from the goals values (i.e., xGpm = (Goals – Own goals) – xG.
