Measuring performances in the Eredivisie – Conversion

Posted on 26 November 2011


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.

Posted in: Eredivisie