Measuring performances in the Eredivisie – Conversion

In the final part of this mini series we will focus on the missing link between creating shots on target and scoring goals: conversion. The first post in this series aimed to assess performances in terms of the raw number of chances created or conceded, while the second post introduced team’s performances in terms of accuracy with their created and conceded shots. To complete the puzzle, we’ll add in the conversion percentages now.

A combined performances analysis in terms of creating chances, finding the target and converting into goals follows the simple principle that the amount of goals scored is a direct result of the number of shots created, multiplied with the fraction of shots on target, multiplied with the fraction of on target shots converted. Conversely, the amount of shots conceded results from multiplying the number of shots conceded with the fraction of on target shots conceded and the average opponent’s conversion.


Offensive conversion

Ranking teams according to the conversion rate of chances creates reveals huge differences. On average, nearly one in four shots on target produced a goal, with 22.4% of shots on target hitting the back of the net.

 The best team is this regard is AZ, who converted 29.2% of their shots on target. On the bottom of the table, Excelsior converted only 10.3% of their shots on target, nearly three times less. In other words, AZ scored a goal per 3.4 shots on target, while Excelsior needed 9.7 shots on target to score a goal.

At the top of the table, a cluster of well performing teams was found around the 27-29% range, with Heerenveen, Utrecht and Roda following the example set by league leaders AZ and title pretenders Twente and Ajax. Although producing by far the most shots on target, PSV’s 24.2% conversion is slightly lower than the leading group of teams show.

More variation is found near the bottom of the table, with RKC and N.E.C. finding some explanation of their recent dip in form and surprisingly low conversion rates for Feyenoord (18.1%) and Vitesse (19.8%).


Defensive conversion

Ranking teams according to the amount of goals conceded per shot on target will reflect both goal keeper performance and defensive performances, making it hard to distinguish the different contribution of both. The table below shows the team’s performances in this regard.

Differences are less outspoken in terms of defense than they are in terms of offense. The top of the table is again for AZ, conceding with only 14.3% of shots on target, while the bottom team, Ajax, conceded a goal with no less than 30.6% of shots on target. Yes, that’s correct, Ajax concede most goals per shot on target. Last season they managed to top the table, with 15.9%, almost half of what they concede per shot on target this year.

Looking beyond the shocking Ajax performance, we can see why Roda struggles this year, giving up a goals with 28.8% of shots on target being converted. An interesting observation is the fact that despite playing a possession based dominant game, Twente are the second best team with 18.1%, even though one might have expected their opponents to have relatively more shots coming from counter attacks, a renowned source of quality chances in terms of conversion. Twente’s excellent defensive performance may highlight Nikolay Mihaylov’s development as one of the top goal keepers in the Eredivisie, as well as Twente’s excellent overall defensive job.


In the end

This post concluded a mini series looking at performances in the Eredivisie. Teams’ performances are broken down into creating shots, finding the target and converting, and on the other hand, to their defensive performances along the same three scales.

When teams do better in one or two of these scales, while disappointing in the other, this may reflect a difference in playing style, formation, player quality, or a ton of other reasons. The interesting thing, though, is that it reveals patterns that may be different to observe with the naked eye.

Most regular Eredivisie viewers would have concluded that Ajax conceded too many goals, but to see them ranked bottom of the table with regard to defensive conversion might be surprising. It also feeds the debate as to how long Frank de Boer will continue to have confidence in Kenneth Vermeer, with 5 million euro summer acquisition Jasper Cillissen on the bench. AZ’s excellent season so far seems reliant on being the most accurate convertors in the league, while also showing the best defensive conversion rate. Is this a reflection of AZ’s strikers and defenders outperforming their rivals, or is AZ overachieving at the moment with a return to average numbers and a dip in form likely to happen? Will Excelsior be able to shift the balance a bit, turning on the offense where they convert to lowest fraction of the league, while sacrificing a little bit of their third place offensive conversion?


This post could never have been created without the support of Infostrada Sports, who’ve provided the data for the analysis.

7 thoughts on “Measuring performances in the Eredivisie – Conversion

  1. Walter

    Great piece. Although Kenneth Vermeer had some outstanding saves it looks like Ajax was better off with Maarten Stekelenburg. Not surprising if you look at the full 90 minutes of their games.

    Looking forward to more in-depth analysis of the causes; playing styles and player ability.

  2. bart

    Excellent stuff … Some notes:
    1. Last year’s full season average was lower (.218 or so) than the average up to now (.224) … I wonder if this relates to defenses/goalies being worse or attackers being better at converting chances? Thus are we seeing more chances and even more goals or are we seeing less chances but more goals?
    2. In both tables there are less teams below average than above average … only N.E.C. and Feyenoord come below the line on both occasions! Interesting is Fey. are top 5 in least amount of goals let in (17) and N.E.C. are just behind with 19.

    RodaJC are bottom with 34 goals let in and AZ top with just 8, percentage-wise AZ are 2 times better but in number of goals that is 4.25 times better!! 4 of Roda’s goals against were let in by Tyton in 2 games; 5 by Prus in 2 games, thus 25 by Kieszek in 9 games. The three combine for an average of .288 in goals/sot.
    Now last year … Prus; 17 goals in 6 games, Collin van Eijk 3 goals in 2 matches (Prus got a red card in the game v Twente, van Eijk came in and was scored against via penalty and then played the last 5 mins, game ended 1-1) and Tyton 30 goals in 27 games. The three combined for an average of .195 approx in goals/sot …
    Now how’s that for a difference, wow. RodaJC lost Tyton, Kah and De Fauw from their regular back 5 … now I know the whole team has to defend but … next thing to analyse is where all the shots came from this year and last year, this will bring us a step closer to seeing what went wrong defensively or if the loss of Tyton alone can be seen as the cause.

    Also interesting to see N.E.C. with and without Cillissen who is considered to be quite a talent … how about the kid in goal at Utrecht or the creaky old guy … 🙂 … ah so much interesting stuff to get in to, too bad a lot is just a very, very small sample size.

    Any ideas on where you will go from here with this data? Is it possible to get data on where the shots came from?

    1. bart

      just a slight follow-up on the RodaJC numbers … (in case anyone is interested, team was picked at random by me)

      This year so far:
      13 games; 34 goals; 2.62 g/game; 118 sot(approx); 9.07 sot/game (approx).
      Last year:
      34 games; 50 goals; 1.47 g/game; 256 sot(approx); 7.53 sot/game (approx).

      % increase in sot/game: 1.20.
      % increase in g/game: 1.78.

      therefore either;
      1. attackers are more efficient with their chances when playing vs RodaJC but average % increase in g/sot is 1.03 overall so it could be but is unlikely.
      2. defense is worse; possible (eg. shots could be from better positions right in front of goal without any hindrance thus resulting in a better conversion rate for attackers.)
      3. goalkeeper is worse; highly likely.
      I’m not great at statistics analysis so I’m sure someone could come up with a more definitive answer. 🙂 Guess I could do this for Ajax … but I have to get back to work. Cheers!

  3. David

    These results are hardly surprising, but surely interesting nonetheless. It shows a few things about Ajax in particular that everyone could suspect: Vermeer is a below-par goalkeeper, making decent saves look flashy but committing far too many errors. His positional sense is horrendous and he looks very shaky defending high balls. He’s pretty good on one-on-ones, though, but still.

    But that’s not the only issue here, of course. Other factors that probably play a big role are: De Boer’s initial reluctance to field any type of holding midfielder (Janssen is anything but), or to select any midfielder that can tackle for that matter; Ajax playing a high line, causing shots on target to be one-on-ones/reasonable chances relatively often; having dinosaur André Ooijer as the only real back-up central defender (especially problematic with the high line). Also, full backs Van der Wiel and Blind are both highly inconsistent. A few of these things can be (or in some cases, already have been) sorted out, but if that’s enough for Ajax to compete for the title remains highly questionable.

    AZ look great this year, very consistent and solid. Like McLaren’s Twente and and PSV from a few years ago (under Hiddink and Vergoossen, for instance), that’s usually enough to ride out a successful title-winning season. They’re the definite favourites this far into the season.

  4. Haris Ansari (@harris6head)

    I think last season, Stekelenburg was not the only one, but the whole Ajax back-line performed extra ordinarily. This season so far, they have failed to perform at their best. I guess last season, Ajax played with 4-3-3 and going with the same this season as well so we can’t suggest that they now need a defensive midfielder.
    Though excellent write up and a good piece to go through. Hopefully PSV would be making life hard for AZ in the race for title. 🙂

  5. Think14 (@Think14)

    Vermeer is definitely to blame mostly for the goals conceded by Ajax, in fact I believe they should have skipped him and gone straight to Cillessen.

    In terms of goals scored, Sigthorsson has been out and hadn’t had enough time to really gel, as well as arguably the next best thing (de Jong out). Klaassen maybe should have been given more of a run in a bit earlier, he looks absolutely wired to score.


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