Defensive Contribution Ratings in SciSports Platform enable in-depth data-driven scouting of defenders
Last December Virgil van Dijk narrowly missed out on winning the Ballon d’Or following a series of rock-solid performances that eventually led to Liverpool clinching the Champions League trophy and finishing runners-up in the Premier League. While the performances of winner Lionel Messi directly translate into goals and assists, the performances of the Dutch centre-back are much harder to capture using traditional football statistics. To overcome this limitation of traditional statistics, we extend the Contribution Ratings module in the SciSports Platform from valuing offensive actions alone to defensive actions!
An important task for football scouts is to assess how football players contribute to the performances of their teams. To assist scouts in this process, we introduced the Contribution Rating metrics in the SciSports Platform last summer. While traditional football statistics such as the number of completed passes or number of successful tackles only consider how often a player performs a particular type of action, the Contribution Rating metrics measure the contribution of different types of player actions by accounting for both their frequency and impact on the match.
The importance of considering an action’s impact is nicely illustrated by the following two video clips. In the first clip, Chelsea’s Fikayo Tomori prevents Burnley’s Jay Rodríguez from scoring with a perfectly-timed tackle in the penalty box. In the second clip, Manchester United forward Anthony Martial tackles Brighton & Hove Albion’s centre-back Lewis Dunk near the halfway line and sees the ball go out of play.
Clip 1. Fikayo Tomori prevents Jay Rodríguez from scoring with a perfectly-timed tackle in the penalty box.
Clip 2. Anthony Martial tackles his opponent near the halfway line and sees the ball go out of play.
While both tackles go down the books as a successful tackle, Tomori’s tackle in the penalty box clearly had a bigger influence on the course of the match than Martial’s tackle near the halfway line.
One action is more valuable than the other
Our widely-used Contribution Rating metrics assess the impact of each player’s actions on the course of a match. Intuitively, these metrics measure how each player’s actions affected their team’s chances of scoring and conceding a goal. The higher the Contribution Rating for a particular type of action is, the more the player has contributed to increasing the chances of scoring a goal or decreasing the chances of conceding a goal by performing that type of action. Actions that yield more favorable match situations receive positive Contribution Ratings, whereas actions that yield less favorable match situations receive negative Contribution Ratings.
To enable scouts to better assess the impact of defensive players on their team’s performances, we have extended the Contribution Ratings module in the SciSports Platform with five brand new Contribution Rating metrics for defensive actions: interceptions, tackles, clearances, fouls, and defensive positioning. The video clips of the Tomori and Martial tackles clearly show the additional insights that the Contribution Rating metrics for defensive actions provide. As expected, Tomori’s tackle receives a higher Contribution Rating than Martial’s. That is, Tomori’s tackle highly decreases the chances of conceding a goal, whereas Martial’s tackle barely has an impact.
Table 1 lists the five types of defensive actions and five types of offensive actions for which Contribution Rating metrics are available in the SciSports Platform from now on.
Table 1. The SciSports Platform reports Contribution Ratings for five types of defensive actions as well as five types of offensive actions. The definitions of these action types are in this SciSports HelpCenter article.
Depending on the match situation, a defensive action receives a positive or a negative Contribution Rating. For example, Federico Valverde’s tackle for Real Madrid in the closing minutes of the extra time of the Spanish Super Cup final against Atlético Madrid received a very high positive Contribution Rating for preventing Álvaro Morata from a one-on-one chance with Thibaut Courtois. The Contribution Rating metric awards positive credit to the Uruguayan’s challenge for vastly reducing Real Madrid’s chances of conceding a goal. However, the Contribution Rating metric does not account for the potential longer-term impact of Federico Valverde’s sending-off.
In contrast, Adam Maher’s foul for FC Utrecht in an Eredivisie fixture against Heerenveen received a negative Contribution Rating for causing a penalty. The Contribution Rating metric awards negative credit to the midfielder’s foul for vastly increasing FC Utrecht’s chances of conceding a goal. That is, Heerenveen’s chances of scoring a goal were much higher from the penalty spot than they were from the location near the edge of the penalty box where Adam Maher unnecessarily commited the foul.
Defensive positioning: Defending is also preventing
The examples above show match situations where a defender prevents an opponent in possession of the ball from becoming dangerous by performing a tackle or committing a foul. However, legendary Milan defender Paolo Maldini once famously said: “If I have to make a tackle then I have already made a mistake”. Defenders often prevent their opponents from receiving the ball and creating goal-scoring opportunities by clever positioning and use of their body. For example, Liverpool centre-back Virgil van Dijk nicely demonstrated these skills against Flamengo in the FIFA Club World Cup final as well as against Chelsea, Tottenham and Wolverhampton in the Premier League.
To fill the gap that the Contribution Rating metrics for clearances, fouls, interceptions and tackles leave, we introduce our novel Contribution Rating metric for defensive positioning to capture this important aspect of defending. This metric goes beyond what existing football metrics offer by measuring a player’s abilities to prevent their opponent from becoming dangerous. Specifically, a player receives positive credit when their direct opponent has a lower impact in terms of Contribution Ratings for offensive actions than can be expected based on earlier performances. For example, Ajax’s Nicolás Tagliafico rates highly on defensive positioning in the Dutch Eredivisie.
Assessing player performances in SciSports Platform
The SciSports Platform reports Contribution Rating metrics for ten different types of actions. Each metric reflects a player’s total contribution per 90 minutes from performing that particular type of action, where the total contribution is determined by the average value per action on one hand and the total number of actions on the other hand. To allow a fair comparison between players who have played a different number of minutes, we first compute the total contribution of all actions of a particular type that a player has performed throughout the course of a season and then normalize for 90 minutes of playing time. To obtain a reliable assessment, we impose a minimum threshold of 700 minutes of playing time and compare a player only with players in the same position in the same league.
The SciSports Platform currently provides Contribution Rating metrics for about 100 domestic competitions in more than 60 countries across the world. Our coverage ranges from the English Premier League to the Colombian Liga Águila to the Qatar Stars League to the Latvian Virsliga to the Japanese J2 League (2nd thier) to the German Regionalliga (4th tier). The Contribution Rating metrics for the players in the covered competitions are updated within a few days after each match with more prominent competitions generally receiving updates slightly faster than less prominent competitions.
Table 2 lists the top-five-ranked players for each of the five defensive actions for different positions in a selection of different competitions.
Table 2. The top-five-ranked players for each of the five defensive actions for different positions in a selection of different competitions.
Virgil van Dijk: Liverpool’s Dutch wall
Since the primary motivation for developing Contribution Rating metrics for defensive actions was that traditional statistics fail to appropriately assess the performances of defenders, Liverpool’s centre-back Virgil van Dijk poses an excellent example to put our Contribution Rating metrics for defensive actions to the test. Our analysis of the 2018/2019 Premier League season shows that the Dutchman ranks second best in terms of overall Contribution Rating across all defensive actions, as can be seen in Figure 1. In particular, the Dutch centre-back stood out in clearances and defensive positioning, while also rating above average for tackles, and interceptions.
Figure 1. Virgil van Dijk ranks second best in terms of overall Contribution Rating for defensive actions among all centre backs in the 2018/2019 Premier League season.
Furthermore, a similar analysis for Van Dijk’s earlier seasons in the Premier League reveals that the Dutchman’s emergence as arguably the world’s best centre-back last year should not come as a surprise at all. A Southampton player in the 2015/2016 season, Van Dijk was already among the five best-ranked centre-backs aged 25 or younger in terms of Contribution Rating for defensive actions alongside Jores Okore (Aston Villa), Chris Smalling (Manchester United), Dejan Lovren (Liverpool), and Gabriel (Arsenal).
Van Dijk 2.0
Although Virgil van Dijk would spend another 1.5 seasons at Southampton before giants Liverpool eventually recognized his excellent defensive performances, the Contribution Ratings for defensive actions enable scouts to identify emerging defensive talents at a young age already. While Liverpool already have Joe Gomez in their ranks and the Dutch national team have youngster Matthijs de Ligt (Juventus), scouts often struggle to recognize defensive talents at a young age. Which youngster have the potential to become as impactful for their team as Virgil van Dijk at Liverpool?
To answer this question, we use the filter capabilities of the SciSports Platform to quickly obtain a list of talented young centre-backs aged 21 or younger that have a high defensive impact in their respective leagues. In addition to the earlier mentioned Joe Gomez and Matthijs de Ligt, we obtain Dayot Upamecano (RB Leipzig), Benoît Badiashile (Monaco), Edmond Tapsoba (Leverkusen), Jules Koundé (Sevilla), Marash Kumbulla (Hellas Verona) and Strahinja Pavlović (FK Partizan) as exciting young talents to watch.
The addition of Contribution Rating metrics for defensive actions such as clearances, defensive positioning, interceptions, fouls, and tackles to the SciSports Platform enables scouts to assess the defensive performances of defenders at a more granular level than can be done with traditional football statistics. Interested in trying the SciSports Platform yourself? Apply for a trial and get started immediately!