The idea for this analysis came from reading Paul Power February post, where he sets out to analyse Defensive Efficiency (Deff). To measure it he lists seven variables, and reasons for his choice. These are:
1. Goals Conceded (GC)
2. Goals Conceded Difference (GC-D)
3. Total Shots Conceded (TSC)
4. Shots on Target Conceded (SoTC)
5. Shots on Target Conceded % (SoTC%)
6. Goals Conceded From Total Shots % (GCTS%)
7. Goals Conceded from Total Shots on Target % (GCSoT%)
In his next post he attempts a classification of teams at that time using 6. and 7. and draws some conclusions.
My take on it
I don’t agree with his choice of 2. which I think this is only useful if one is trying to compare Home vs. Away Deff performance, not overall one. I also have doubts about the contribution of 5. SoTC%; I’ll leave both out of my analysis.
My analysis has a similar aim, but I am going to split Deff into two components, Defensive effectiveness (Deff), and Defensive efficiency (Deff%), and analyse them separately. The first measures how much a defence in effective in restricting shooting opportunities to opponents; the second its efficiency in preventing goals being scored.
Defensive effectiveness (Deff)
For this analysis I have taken the list of variables that follows. As well as Totals for Goals, Shots and Shots on target, as done by Paul, I have added Home and Away figures. These would help me cluster teams that have a similar defensive profile. (PS As would have figures for Goals conceded In and Out of the Box, of course, if I had them)
HGC Home Goals Conceded
AGC Away Goals Conceded
TGC Total Goals Conceded
HSC Home Shots Conceded
ASC Away Shots on Target Conceded
HSTC Home Shots on Target Conceded
ASTC Away Shots on Target Conceded
TSC Total Shots Conceded
TSTC Total Shots on Target Conceded
The data comes from the 2013 EPL, as given by the website Football Data (link),and is shown in the table below:
The Deff analysis
To classify teams according to these metrics I am going to use the Cluster Analysis method I have used in my previous post . The results are shown in the picture below. The data has been normalised: high values are shown in red and low in green (best performers), as in the colour scale shown.
From left to right, the following picture shows:
- The order in which team have been ranked with respect to the performance parameters
- A heat map that shows the normalized values of these parameters
- A dendogram that shows how teams have been clustered
To my surprise, Arsenal, whose defensive performance was much criticised during much of the season, tops the list. Also Man Utd, the champions, are not among the best defensively, and belong to the second best cluster of teams that share a similar defensive profile. Stoke is the surprise entry in this second cluster – not bad for a team who just avoided relegation to be in (just) with the champions. But I guess this can be explained with the fact that they score and concede few shots and goals (sorry, I haven’t got time for a deeper analysis).
As for the bottom half of the table, nobody would be shocked to find Reading at the bottom, and alone because so much worse than all the others relegated companions. But I guess not many would have expect ed Swansea to be just above them. I seem to recall too many heavy defeats though. I’ll leave you to reflect on the other teams positions.
The Deff% analysis
This analysis is aimed at classifying teams in respect to their Deff% and clustering teams with similar profile. So, while in my first analysis I have taken values, I now take ratios % of Goals conceded o Shots conceded.
- HGC% = HGC/home shots
- HGCT%=HGC/home shots on target
- AGC%=AGC/away shots
- AGTC%=AGC/away shots on target
- TGC%=TGC/totals shots
- TGCT%=TGCT/total shots on target
The results are shown in the figure below:
There are some discrepancies between the two images, as the one on the left show the ordering clusters and not of individual teams (clustering is not an exact science). What is clear, though, is that Chelsea and West Ham have the best Deff%, and that Southampton, Wigan and Newcastle have the worst one in that order – but there is not much to choose between them. Could this be the main reason for the Toons steep fall from last year grace? I’ll leave you to ponder about the other results. I’ll just comments on some of that really stand out.
High flying Tottenham (at least for most of the season) is just above the trio of relegated teams . This probably accounts for the missed Champions league spot, and something AVB will need to address in order to improve performance for next season. I am sure that he knows that despite his (apparent) dislike of statistics.
Arsenal, appears to be the odd team out in his cluster on account of his poor Home performance , which is of a bottom three placing. But is obviously lifted by his outstanding Away one.
And, finally,it appears that it wasn’t because of their Deff% that QPR and Reading were relegated. Looks like they may have conceded some decisive goals in their fight for salvation.
So, which team have the best and worst defensive record? A combined cluster analysis of the two metrics should in theory give the answer. But I had problem getting a meaningful and consistent classification, probably on account of the mix of values (Deff) and ratios (Deff%). So, I /we’ll have to do it by inspection of the combined heat maps below, and views are bounds to differ:
Mine is that Arsenal does not deserve top spot because of his very poor Home record in conceding goals. Man City appears to have the best combined record, followed by Man Utd, and Chelsea, the latter on account of its best Deff%.
As for the the teams with the worst record, the picture is much less clear, and contrasting results make it rather confusing. Swansea is a case in point , with one step from the bottom with regards to Deff, and in third position with Deff%. And then there’s Tottenham, fifth in the League table, and in the top cluster for Deff, but near the bottom in Deff% – where is its true place? Even worse is the dilemma facing who wants to judge the relegated teams, with Reading with the worst Deff of all, and Deff% near mid-table. And what about Sunderland? I’ll leave you to make up your own mind on this and the other teams.