A House Move

I, along with a couple of other pretty decent analysts, have made the move across to http://www.statsbomb.com/ – so any future articles will be published there.

If you like what you have read here on my blog then I’m sure you’ll like the new place even better, so why don’t you follow me across……..

Thanks
Colin

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How do Headers compare to Shots?

In performing some of my shooting analysis work I have struggled with how best to deal with headers.

It is obvious that, on average, headers are taken from locations closer to goal than non-headed attempts on goal (these non-headed attempts will be defined as “shots” during the rest of this piece).  That alone would be enough to ensure that we shouldn’t group together headers and shots when undertaking any aggregate analysis.
The combining together of shots and headers is even more problematic when we consider that they may have different outcome profiles even when taken from similar locations.  This realisation has had some recent airings on Twitter, so I thought I would use the data that I have collected from the Big 5 leagues last season to put on record just how a header compares against a shot.

Summary Numbers

Heads1

When looking at all shots and all headers we can see that there is only a negligible difference in the amount of each type that are on target (34% of headers vs 33% of shots).  However of those on target attempts, a header is more likely to be scored than a shot (12% v 9%).  It is no surprise to see that headers are blocked much more infrequently than shots; shots are blocked approximately three times as often as headers.

So, if headers are scored at a higher rate than shots, does that mean that, given the choice we would prefer our team to be having a headed attempt at goal rather than a shot struck with the foot?

I would suggest that the answer to that question would be “no”.  The main driver of why headers are converted more frequently than shots is due to the location of where the attempts originate.

Location of Attempts

Heads2

Almost 95% of all headers are taken from the central portion (within the width of the 6yd box) of the penalty area, this compares with just 25% of shots.  Virtually no headers are taken from outside the penalty area; whereas more than 54% of shots originate from these longer distances.
At this stage, it’s now easy to see why headers are converted with greater frequencies than shots.

Direct Comparisons

How would the conversion rates for shots and headers compare if we looked at like for like, ie removed the location basis that is inherent with headers?

Inside 6yd box

In6

Shots taken from inside the 6 yard box are converted at 40%, compared to less than 25% for headers.  So within these close range locations headers were scored only 62% as often as shots were.
One other takeaway from this grouping of shots is that less than 40% of headers from this extremely close location were put on target.  Presumably this is indicative of the pressure that is applied to headers that are attempted from such close range.

Other Central Locations Inside Penalty Area

InC

This time we are looking at shots within the central portion of the penalty area, but beyond the 6 yard line.
Once again, shots are converted at vastly superior rates to headers.  This time the conversion rate for shots is almost double that of headers at 20% and 10% respectively.  As before, we can see the difficulty that headers have in even just hitting the target.

Sides of Penalty Area

InS

Now turning our attention to shots / headers that were struck from the sides of the penalty areas (outside the width of the 6 yard box) we can see the familiar pattern continuing as yet again shots are converted at twice the efficiency of headers.

Summary

In writing this article I set out to determine how much less likely a header was to score than a shot.  Without adjusting for shot location headers are scored at a greater rate to those of shots.  However, in respect to this particular topic the devil is in the detail as we determined that when shots and headers that were struck from similar places were compared the conversion rate for headers was only approximately half of that for shots.
This is a fact that should be remembered by anyone interested in the analytical side of football

Perhaps I could go as far to suggest that with shots and headers having such vast differences in conversion rates, perhaps the time has come for shots and headers to be disclosed separately in post match statistics instead of them being aggregated together as is the current norm.

Arsenal and their Pretty Pictures

@JoshJMTG said this morning after reading the locations article “So wait, you’re telling me that the trouble with Arsenal really is that they always try to walk it in?”

Well, it gets worse, or maybe that should be better.  I was playing around with some dates and managed to create this very pretty looking Arsenal picture:

Arsepretty

Believe it or not, the above is the heatmap for every single (all 433) shot that Arsenal took in the EPL after the 27th October.
They didn’t take a single shot from wider than the outsides of the penalty area and they never took a single very far out shot either.  Over a period of seven months that is pretty amazing.

Just as a means of comparison here are the images for a couple of other teams over the same period:

Tottenham

Tott

Man United

Manu

and, Liverpool

Live

So, Arsenal certainly win the prize for the Prettiest Picture, although perhaps sometimes just a little variety may be beneficial to them.

The West Ham Phenomenon

In my previous article where I looked at the average shot position (exc penalties and headers) of the leading strikers last season in the Premier League the average position of Kevin Nolan’s shots stood out for me.
Nolan’s average shot position over the course of the season was closer to the goal than any other player in the entire league who had more than 65 shots.  I don’t watch that much of West Ham, and so that finding did surprise me somewhat.

Following some discussion on my Twitter timeline with @footballfactman @them_l_g  @basstunedtored it was suggested that the taking of shots close to goal was likely to be a deliberate tactic by Sam Allardyce.  Allardyce’s interest in football analytics is well known, and it certainly seemed a plausible explanation.  It could be possible that someone has told Allardyce that taking long range shots may not necessarily be the most optimum tactic (really?).

I thought I would test this theory.

So I looked at the average shot position of all the shots taken by the 20 teams in the Premier League last season.  I used the same methodology as in the previous article, and so I excluded penalties and headers.

As expected, given the large number of shots taken, all the teams have a fairly close average shot position.  In order to help identify different teams I have zoomed in on the graphic below; the black dot is the penalty spot and the red line is the outline of the penalty area.

WH

And look what the data clearly shows.

Three teams’ average shot position was much closer to the goal line (relatively speaking) than all the other teams in the Premier League.
Those three teams are the two Manchester teams, who finished first and second, and West Ham, who didn’t.

In fact, only six teams had average shot positions which originated from inside the penalty area.  Those teams’ final league positions were 1st, 2nd, 4th, 6th, 7th and 10th (West Ham).

Ignoring West Ham there appears to be a pretty strong correlation between shots originating from close to the goal and league position.  Of the strong teams, only Chelsea and Bale Tottenham had shots that came from outside the penalty area on average.  I will generalise therefore and say that, as a whole, it seems that the stronger the team the closer to goals their shots are taken.

With this in mind, it seems hugely significant that West Ham were the team that actually had the closest average shot position to the goal line.  Such a close position just would not be expected from a team of their ability.

To me, it seems clear that Sam Allardyce has introduced a deliberate strategy of trying to shoot from close to goal.  Although this seems obvious, it is clear that there are not many other teams in the league who have, so far, decided to adopt a similar strategy.

Average Shot Location for Leading Strikers in EPL

Following on from an image I tweeted a couple of days ago, I wondered what it would look like if headers, as well as penalties, were removed,

I decided to include all players that had more than 65 shots (excluding headers and penalties) last season.  This gave me a manageable list of the 26 players that took the most shots in the league last season.

How it works

The distance from the goal line to the marker is the average distance out of all shots that the player took.

The distance across the pitch from the penalty spot was a little more difficult to present as it would be wrong to use a simple average – had a player took two wild shots, one from the right and one from the left the average would appear right in the middle of the pitch!!

What I eventually decided on was to take the average of the absolute values of the distance from the penalty spot for each shot.  To then help spread out the data points I have plotted the data point to the side of the penalty spot which seen the majority of shots taken for that particular player.

NoHeadsPens

So what does it tell us?

Taarabt and Lampard took shots that were farthest out on average, it certainly appeared that the QPR player adopted a “shoot on sight” policy this season.  It is not surprising to see Bale and Cazorla shooting from so far out on average.

Wayne Rooney is interesting, his average shot position is outside the penalty area as well.  I don’t have data for previous seasons, but I would guess that if this image had been created last season that his average shot position would have been inside the area.  I guess that is what happens when his role is now to play as second fiddle to Van Persie and we can see how much closer to the goal Van Persie’s average shot is as a result.

The marker closest to goal certainly surprises me.  I wasn’t expecting to see Kevin Nolan’s average shot position to be from a much closer position than any other player, strikers included.  I’m only hypothesising here, but is this average position as a result of playing off Andy Carroll’s knock downs?
Whatever the reason Nolan was certainly making a point of playing a very advanced role.

Across the capital in North London, Giroud definitely can’t blame shot location for his pretty poor returns this season.  He couldn’t have asked for a better average shot location position.

Arguably Suarez’s reputation for shooting from non-optimum positions is deserved, excluding Bale his average shooting position is wider than any other player.

Who was the Most Accurate Finisher in EPL?

In this article I’m having a look at which player was the best finisher in the Premier League last season.  By “best finisher” I mean the player that achieved the highest percentage of their shots on target.

Likely Candidates?

Given the fact that Robin van Persie finished top of the Premier League goal scoring charts with 26 goals some might think that makes the Flying Dutchman was the most accurate finisher.
Others may well be of the opinion that due to the amount of long range, and therefore difficult shots, that Gareth Bale took, yet managed to bag 21 goals in the process, means that he could be described as the most accurate finisher in the league.
Although Bale was close to earning the title of most accurate finisher, using a methodology that I have created neither Van Persie nor Bale achieved this feat this season.

Read on to see which player was the most accurate with their strikes on goal.  But before you get there, have a guess at who you think it might be.

The Methodology

First of all, a little introduction to the methodology used.  I looked at each shot that was taken in the Premier League this season and divided the locations of those shots into 4 zones.  Those zones were:
– Inside Pen Areas Central (yellow)
– Inside Pen Area Sides (red)
– Outside Central (blue)
– Outside Other (green)

zones

For each of the zones I looked at the overall 2012/13 Premier League average for accuracy, ie shots on target.
The total league average for the 4 zones are as follows:

Untitled

So the average player has 45% of the shots they strike from the Inside Central zone on target, and this then reduces to 41% for shots taken from just inside the edges of the penalty area and finally down to 31% or 32% for shots from outside the area.

We will quantatively decide which player had the most accurate shot ratio over the course of the season by combining those average accuracy percentages with the actual number of shots that each player took from each of the four zones.  The real benefit of using this measure is that it takes into account the location of the shots and therefore the difficulty that the player would have experienced in getting his shots on target.

Tale of Two Gunners

A look at two of Arsenal’s forwards provides an interesting demonstration of the importance of shot locations.

Podolski had 35% of his shots on target and Giroud managed to get 36% of his shots within the frame of the goal.  If we were armed with only those stats, which would be as much information as we would traditionally use, then it would be reasonable to reach the conclusion that the French striker finished his chances slightly better than his German comrade.

However, if we were to look at the location of where the shots originated from for each of the two strikers I’m not sure that we would still reach that conclusion.

aresnal

Now we have the benefit seeing the breakdown of their shots, we realise that a massive 61% of Giroud’s shots came from the optimum location, Inside Central.  It is obvious that Podolski’s achievement of getting 35% of his shots on target was a much better achievement due to the fact that he had less than 40% of his shots from that same prime location and much more from outside the penalty area.

Don’t worry, I’m not awarding the crown of Most Accurate Finisher to either of the Arsenal strikers but hopefully my look at part of the Arsenal strike force shows why the location of shots are so important when evaluating a striker.  Bare shots on target data simply cannot tell the full story.

From the above table we can instinctively tell that Podolski has achieved a higher accuracy rating than Giroud, but can we quantify this?
Thankfully, yes, I feel that I am now in a position to be able to quantify just how much better his performance was than his French strike partner’s last season.

Using the absolute number of shots that the players had in each zone and multiplying those by the league average accuracy rate for the respective zone gives us the total expected number of shots on target that each player would have expected to have had (on the basis they had league average accuracy).  We can then compare to the actual number of shots that they managed to hit the target with and this Actual number divided by the Expected gives us our Accuracy Ratio (AR).

A worked Arsenal example may aid the understanding here.

Podolski actually had 19 shots on target, and when we looked at the mix of his shot locations we see that the average Premier League player would have had 17.14 of them on target.  19 Actual shots on target divided by 17.14 Expected= 1.11, ie Podolski had 11% more shots on target than the average player given the mix of shots he took.

summ

We can see that Podolski achieved an AR of 1.11 and Giroud 1.03.  When you bear in mind that the entire league average of all players who took a shot, including defenders, Aaron Ramsay and Stuart Downing, was 1.00 you can see just how poor a season Giroud had in terms of trying to hit the target.

Bottom of the Table

Before we look towards the top of the table, I thought it would be interesting, if not a little cruel, to see which players languish at he bottom of the AR table.
To ensure that players who took relatively few shots during the course of the season don’t interfere with my analysis I decided to just include players who had taken at least 38 shots during the season.  Please note that penalties are excluded from all of the figures quoted in this article.

bottom

We’ll not labour too long at the names on the above list, as many of them won’t come as a surprise to football watchers.  However, when your job is to primarily get the ball in the net (I’m looking at Danny Welbeck and Andy Carroll to a lesser extent) and you are sitting in the bottom dozen accurate finishers across the league as a whole then you probably should have some explaining to do to those paying your wages.

One name which appears on that list and may surprise some, but it’s not an error, is Michu.  How could a player who finished 5th in the Premier League goalscorers table, and who had a great season, at least according to all the traditional media outlets, be that poor of a finisher?
The purpose of this article is not really to reason why but it certainly appears that Michu lucked out in a big way, both in terms of the amount of shots on target that turned into goals and also the fact that 66% of his shots came from that golden Inside Central zone.

At the Top

We’ll now turn our attention to the top of the Accuracy Ratio table.  Note that at this stage I have still hidden the player with the highest AR at this stage, and that Bale actually finished 2nd in the table with an AR of 1.54.
Take a second to pause and consider just how good an AR of 1.54 is; had he been the average league player faced with the shots that he took during the season Bale would have had just over 47 shots on target – instead he managed a hugely impressive figure of 73.

top

44% of Gareth Bale’s shots were on target, and when you consider that so many of his efforts were long-range attempts (59% of all his shots were outside the penalty box) you can realise just what a Shot Monster (term created by @mixedknuts) Bale was for Spurs during the 2012/13 season.  At this stage, we’ll not consider what sort of a season Spurs would have had if Gareth Bale was merely human.
I guess not too many would have expected to see Anthony Pilkington occupy the lofty position of 3rd in this particular table.
A little further down, Chicarito underlined just what a great finisher he is with an AR of 1.47, comfortably ahead of Van Persie who achieved 1.30.  Perhaps, given his AR, he can feel aggrieved that he doesn’t get a huge amount of pitch time.
You can browse the list in your own time, but one last name that I want to mention is Daniel Sturridge.  For some reason he never seems to get the credit he deserves and yet he showed terrific shooting skills to finish the season on an AR of 1.40.

The Winner

Now it’s drum-roll time.  Given the above list contains 27 top finishers, who is missing from that list and therefore is the holder of the Number 1 position in terms of shooting accuracy in the 2012/13 Premier League?

That man is Shaun Maloney, all 5ft 7inches of him, who unfortunately wasn’t able to help Wigan avoid relegation.  Despite only scoring 6 goals from 55 shots his shooting accuracy was better than anyone else in the Premier League this season.

maloneypic

Maloney managed to get 45% of his shots on target, a slightly better percentage than Bale.

maloney

But it was the location of the shots that he took that seen him win the crown of the Most Accurate Finisher with a terrific AR of 1.59.

He had the misfortune to have just 15% of his shots from the Inside Central location, even there the league average for shots on target is only 45%.  So to achieve an accuracy of 45% from all of his shots, when we bear in mind that 57% of his shots were from outside the area, demonstrates just how sweet a right foot the little Scottish winger possesses.
Needless to say, it’ll be a shame if Maloney isn’t playing Premier League football next season.

As an aside, if we were to ignore shot location, the players that had at least 38 shots and had the most shots on target as a percentage of all their shots were Chicarito and Steven Fletcher – both achieved 51% on target.

 

EDIT – For full disclosure, I have noticed that I made an error when calculating the league average for each of the zones.  The correct figures should be

corr

Using the correct numbers doesn’t change any of the placings or subatantially change any of the ARs so I’ll keep the article as it was published originally as the essence of the article is still exactly the same.
The author will be even more careful when dealing with large amounts of data in the future.