Trying to Find the Defensive Strengths and Weaknesses of Clubs in the SPFL
Written By: Matt Rhein @TheBackPassRule
Analytics in Scottish football is no longer a tiny niche corner of the internet. Managers are quoting “advanced stats” in post-match press conferences , analytics-themed articles being featured in official club programs, and even helping to win a club promotion. It seemed that Scottish football has been behind the “Auld Enemy” of England in terms of the mainstream acceptance of analytics in football and advances in the practice and methods of football stats, but that gap is closing.
Football analytics literacy is at an all-time high in Scottish football, but there has been debate about whether the public sphere of football analytics in general has plateaued. Some believe that we have hit the saturation point with what data is publicly available. Most know what expected goals is and what the limitations and advantages of the metric is. There does not seem to be much room to improve something like expected goals anymore, so the whole of public football analytics is just sort of waiting for the next advancement in the field (those working privately for a club or a consulting firm probably laughed uproariously at that sentence, thinking of the advances they have already made, jerks.)
One area where there still seems to be room for plenty of advancement in football analytics is measuring an individual’s contributions to his club’s defense. There are more data points for a player’s defensive activities than ever before, with metrics such as tackles won, aerial duels, and others now available. However, there has yet to be anything to show the link between having high numbers in these metrics and a team’s defensive strength. These metrics are certainly intuitive when thinking of a defender’s performance, but perhaps there are other ways we can look at what parts of the pitch a team is strong or weak at defensively.
Expected goals was mentioned earlier, and we can use the xG a team concedes to help measure the strength of their back line as a unit. This does not tell us much about what individuals or areas for a club’s defense are weaker or stronger. We need to get more finite to perform this type of analysis. Some believe this is not possible without something like tracking data, yet with borrowing an idea from football tactics and looking at the data we have in different ways we can try to go deeper.
If you are a frequent visitor of football tactics sites such as Spielverlagerung, you are likely familiar with the idea of the five half-spaces. This divides up the field into five equal sections, the left wing, left half-space, middle, right half-space, and right wing. Thanks to the wonderful folks at Stratabet, we have the locations of every shot and key pass from the Scottish Premiership. We have used this data to create an xG model, which we can use to gather various team and individual metrics and give us more information about where teams are most vulnerable.
We can map the xG of the locations where teams concede chances, but those tend to generally follow similar patterns team to team (every team needs to calm down with the shots outside the box). However, the locations of where in the five half-spaces Key Passes are conceded might tell us more about where the opposition is looking to exploit a team’s defense. If we add expected assist values to where clubs are conceding key passes, we can see where they are able to stifle their opponents defensively and where they might be weak.
With these ideas in mind, let us look at how it applies to the defenses of the Scottish Premiership. Starting on the left wing, we see that Celtic has conceded both the lowest number of key passes as well as the lowest xA per Key Pass from the left wing. Given that we have nearly universal agreement that Kieran Tierney is the best left back in the league, Celtic having the lowest xA per key pass may show that we are on to something here.
Looking at the left half-space, we again see Celtic conceding lower than average key passes compared to the league, but those key passes are leading to a higher than average chance of scoring. Given some of the defensive frailties Celtic has been purported to have, their metrics for the left half-space stand to reason. Aberdeen has the lowest xA per key pass in the SPFL so far this season. With the emergence of Scott McKenna this season, this metric supports the notion that the young Scottish center back has been integral to the Dons this season.
Motherwell have found themselves in two Cup Finals this season and an improved league campaign. Much of the success the Steelmen have found has come from the back, with a solid defense lead by the likes of Cedric Kipre and Charles Dunne. This is shown in these numbers, the Motherwell averaging the lowest xA per Key Pass from the middle half-space, though they do concede a slightly higher than average number of key passes from there.
At the time of writing, Hibernian was within touching distance of a European place in the table. Neil Lennon’s side have likely surpassed most expectations after earning promotion from the Championship last season. Looking at their xA Conceded per Key Pass for the right half-space, we see the Hibees with the lowest and second lowest xA per key pass. This may be a surprise with the likes of Efe Ambrose, who previously had a bomb-scare reputation. Ambrose and company have kept the Leith side secure in the back and helped them be a contender for a Europa League qualifier.
It has been a rough season for Ross County this season, with one match to go they sit at the bottom of the table. If they are not able to move up, they will spend next season in the Championship. However, there has been one bright spot for the Staggies this season and that was Jason Naismith. The 23 year old Scottish full-back has spent most of the season patrolling the right side of the County back-line. We see that the Ross County defense has allowed more than the league average number of key passes from the right wing. Yet, the average xA of each key pass from that right wing is below average and the lowest in the league, thanks mostly to Naismith's form this season. If the Staggies are not able to stay up in the Premiership, Naismith will likely attract the attention of the other top flight clubs in Scotland.
While we talked about who seemed to be the strongest in each of the five half-spaces in the SPFL Premiership, but we can apply the inverse to see where a club may need to improve their back line. If a club, such as Hamilton on the left wing, is allowing towards the highest number of Key Passes and highest xA per Key Pass from that area, they will know they either need to bring someone off the bench or find a replacement for the player in that area. Limiting the number and type of chances your opponent gets is the name of the game on defense, and with this metric, we see where you can and cannot attack them to be successful.
This article was written with the aid of StrataData, which is property of Stratagem Technologies. StrataData powers the StrataBet Sports Trading Platform, in addition to StrataBet Premium Recommendations.