Tuesday, January 31, 2012

Everton and Fulham, Quo Vadis? Data From This Season

On this side of the Atlantic, the football news that received quite a bit of attention over the past few days was Friday's FA Cup tie between Everton and Fulham, featuring Clint "Hat Trick" Dempsey, Landon Donovan, and Tim Howard. Everton won, and as SI.com put it
Landon Donovan etched his name further into Everton lore with two assists in the Toffees' FA Cup victory over Fulham. The match featured Donovan and fellow U.S. alpha dog Clint Dempsey going head-to-head as opponents for the first time since an MLS match between the Los Angeles Galaxy and New England Revolution on May 6, 2006, and unlike that day, when Dempsey's side rolled to a 4-0 victory, Donovan stole the show with his contributions from the right wing.
Coming into the game, you would have been hard pressed to pick a favorite, however. So far this season, both Fulham and Everton have been solidly mid-table teams, sitting on 26 points to date. And when you look at the trends in goals scored and conceded (in the graph below), the two clubs look eerily similar (dots are individual matches, and the lines are the trends over time). The trend over the first 20 weeks of the season puts both of them at just over one goal per match scored and conceded, and the table seems to reflect their similarities.*

Interestingly, the data show that Everton's defense has tightened up somewhat in the second 10 weeks of the campaign, while Fulham's has stayed mainly level (with the exception of the 0-5 home defeat against Manchester United).

One question, of course, is how these very similar records have been produced, so I took a quick peek at shots taken and conceded, along with one of my favorites, offensive and defensive efficiency (as measured by the goals to shots ratios).

Monday, January 30, 2012

Zero Sum Games: Some Pictures of Shot and Goal Differentials in the Premier League This Season

Football's a simple game. If you score more or concede less than the other side, you win the match. So I thought it would be worth taking a look at which teams have been doing better than their opponents. The simplest way of doing just that is to calculate differentials for the stuff that matters most - goals - and the stuff without which the stuff that matters most usually doesn't happen (that would be shots, of course). 

So, here, first of all are goal differentials by match, for the 20 Premier League clubs during the first 20 weeks of this season.

One thing that's immediately noticeable, regardless of name, is how few clubs consistently produce positive goal differentials. The season's top two (Manchester) teams clearly stand out, both for their consistency in producing positive goal differentials as well as the size of these differentials. But other trends are quite visible as well - compare, for example, Sunderland and Fulham. Sunderland's matches have been decided by just a goal for most of the season, while Fulham have had massive swings, it seems. Or compare Bolton and Blackburn, two clubs that are stuck in and around the relegation zone. Blackburn's consistent losses have been relatively small compared to Bolton's sizable (but also decreasing) defeats. Finally, Arsenal's terrible early season and recovery but weeks 10-12 show up very nicely, as does their subsequent decline.

Whatever you may read into these goal differentials, they're kind of fun to ponder, as are the following differentials on shots taken by each club in each match.

Friday, January 27, 2012

Manchester City's Offensive Production: A PS

Here's a short PS to my earlier post about Manchester City's offensive performance so far this season. It provides a summary of shot creation and finishing for the first and second 10 weeks of the season. Dots mark the club's performance in an individual match. The number next to the dot indicates the week. And the dark blue lines tell us where half of all clubs (the 50th percentile of the league) stand in shots or goal to shot ratios by Week 10 or 20, respectively.

The pictures tell the story (hence the post). While virtually all of City's performances during the first 10 weeks put them in the upper right hand corner - among teams that took more shots and finished better - the second ten weeks of the season to date paint a more mixed picture.

Thursday, January 26, 2012

What's Ailing Arsenal? Diagnosing the Gunners' (Offensive) Weakness With Some Data

Arsenal have had a most unusual season of highs and lows. After a rough start to the campaign, the ship seems to have steadied. Robin van Persie is on pace for a record setting season; his 19 goals so far are only one less than last year's 20 scored by Golden Boot winners Carlos Tevez and Dimitar Berbatov. And iconic legend Thierry Henry has been signed on loan to lend some offensive firepower, experience, and spirit. At the same time, the 36 points Arsenal have accumulated at this point in the campaign are the fewest during Arsene Wenger's reign. This Arsenal season has been anything but boring for outside observers and surely nerve-wracking for supporters.

But what do the numbers tell us about what the Gunners are producing on the pitch? Have Arsenal improved? What have they been doing well? Is it offense, defense, both, or neither?

To start, let's take a look at the trends in the stuff that ultimately matters the most: scoring and conceding goals. The graphs below show the numbers of each, with a best-fitting trend line superimposed to see if there is a pattern to Arsenal's performance over the course of the season to date.

It only takes one quick glance to figure out that Arsenal's offensive season has been one of a significant up and a notable down. Arsenal started the season without much offensive success but saw a significant increase in offensive output all the way to Week 10. But that high point didn't last; instead, it gave way to a steady slide in offensive output all the way to the halfway point of the season. As it stands now, Arsenal's offense is not doing nearly as well as it was 8-10 weeks ago.

In some contrast, Arsenal's inconsistent defensive displays that marked the start of the season seem to have been overcome over the course of the last three months. Halfway through, SzczÄ™sny & Co. managed to steady the ship, put in consistent performances, and produce 7 clean sheets in the process.

Taken together, this produces a mixed picture of where Arsenal stand at this point in the year. On the offensive end of the pitch, after improving significantly two months into the season, and despite van Persie's record-setting goalscoring pace, the Gunners' sharpshooters have been silenced somewhat. In contrast, their defense have allowed only .7 goals on average in the last 10 matches.

So what has happened to Arsenal's offense? To answer that question, lets' look at chance creation and finishing - two of the most critical dimensions of offensive performance for any club.

Tuesday, January 24, 2012

Manchester City's Goal Machine: Is It Slowing Down?

When Manchester City dispatched Manchester United in commanding fashion earlier this season, the City steamroller was powerful, efficient, and impressive. It looked downright unstoppable. As Kevin McCarra noted the day of City's 6-1 trouncing of United in The Guardian, "For the football world at large, it is more significant still that City have 33 goals from nine league games. A club of such means does not usually inspire fondness from neutrals, but only a curmudgeon could fail to appreciate the accomplishment of City." Today, two months later and after beating fellow contenders Spurs 3-2 over the weekend, City still sit atop the Premier League, seemingly the team to beat this year.

So all is well at the Etihad, or so it seems. But are City still in a league of their own? The data below tell us that, despite the impressive goal difference revealed by a glance at the league table, City's offensive steamroller has slowed down. In fact, as a comparison across all 20 clubs shows, City is the club that has seen the most significant deterioration in offensive performance since the early days of the season.

Don't believe me? Take a look at the following graphs of some simple statistics. The first shows clubs' goal production for each week of play, up until Week 20 of the season. The dots show the number of goals; the lines show the trend. 

Clearly, between Weeks 1 and 10, City were on an astonishing run. But, as the numbers reveal, this trend was not sustained. Statistical tests show that the trend in goals for City this year are best approximated by a quadratic function. This tell us that, after high level of scoring for the first half of the first half of the season, there has been a noticeable decline in City's offensive production.

Just in case you want to take a look at City's numbers in greater detail, here they are again for good measure.

Of course, any reasonable person might ask "How could there not have been a decline?" They were off the charts, and this may simply have been unsustainable. So if the team over-performed early in the year, what we are looking at is simply regression to the mean, and we should see a decline in performance across different dimension of offensive play as the season wore on. So let's take a quick look at two indicators: first, chance creation; second, efficiency. 

Monday, January 23, 2012

Goal Trends In The Premier League: The Inverted U of the 2011/12 Season

With the pressure and excitement of each and every week's matches, it's sometimes easy to lose the overall plot of how a season has evolved in the league as a whole. Since we are just past the halfway point of the season, I thought I'd take a look at a couple of trends in teams' output in the Premier League this season.

The data show the average goal and shot production over the course of the season for each week of play with data for the first 20 weeks of the season. In addition, I superimposed the best-fitting trend lines.

First things first: let's look at goals. After we saw an increase in goals from slightly over 1 per team and match in the first few weeks of the season, goal production increased markedly through Week 10 to around and even above 1.5 per team and match. However, since Week 10, we have also witnessed a decline to lower levels. Statistical tests reveal that this pattern in the data is best approximated by a quadratic function, suggesting that goal production in the Premiership has followed an inverted U this year.

One natural question is "why"? Did teams start taking and allowing fewer shots on goal in Weeks 11-20, or did strikers forget how to find the net? Let's take a look. The next graphs show the average number of shots per team and week as well as the goals to shots ratio - how efficiently teams converted shots to goals.

Wednesday, January 18, 2012

Why Match Of The Day Is Bad For Understanding Football

Note: This post comes with a Geek Alert!

Television has had a profound influence on football: the players, agents, business models of clubs, the relationship between league play and international football - you name it. Importantly, it also affects how people see and understand the game. Few television programs are more loved by fans than highlight shows like the BBC's Match of the Day, which has been on the air with interruptions) since 1964. MOTD is the Granddaddy of shows (like the German ARD's Sportschau or Fox Soccer Channel's Premier League Review Show that highlight all the day's action for easy consumption. It's not hard to imagine why most people would opt for watching an episode of MOTD over reading this blog or staring at an Excel sheet to understand football. Highlight shows are fun to watch, and their entertainment value is inevitably higher than watching two mid-table teams grind out a 1-0 result over 90+ never-ending minutes. It's kind of like the McDonald's version of watching a football match.

Highlight shows like MOTD are fun. But, curiously, they also make it more difficult for viewers to appreciate what really happens on the pitch during the 90+ minutes of a match.

Tuesday, January 10, 2012

Transfer Window Benchmarking II: Defensive Performance in the Premier League

As a follow-up to yesterday's post about offensive performance in the Premiership so far this season, here's a simple graph summarizing clubs' defensive performance this season. Naturally, it's limited in what it can tell you - all stats are - but the picture does provide some interesting pieces of information. On the vertical axis, we see the average number of shots conceded per match; the horizontal axis allows us to locate clubs' defensive goal to shot ratio (the ratio of goals to shots conceded) per match.

As before, recall that the different quadrants reflect different performance profiles. Clubs in the upper right hand corner both conceded lots of shots and allowed their opponents to convert them to goals very efficiently. In contrast, teams in the lower left hand corner didn't allow too many shots and prevented their opponents from scoring efficiently (the green lines denote the league medians - 50% above and below). So, on defensive performance, we want our club to be in the lower left hand corner and certainly not in the upper right hand one.

So what do we see? As on offensive performance, Manchester City are this season's standouts so far. They have allowed the fewest shots and typically haven't allowed their opponents to score off the chances they did create. While City are in a league of their own, Liverpool, too, has had a very strong defensive first half of the season.

At the other end of the table, we see that Blackburn, Fulham, QPR, Wolves, Norwich, and Bolton have allowed similar numbers of shots per average match (between 15 and 16), but Blackburn (as well as Wigan) have been particularly permissive when it comes to being scored on. Almost 1 of every 6 shots taken on the Rovers' and Latics' goal found the net; in contrast, only one in 12.5 shots crossed the line for Manchester City, Tottenham, Manchester United, and - surprise - Swansea. Clearly, the Swans' defense (and their terrific goalkeeper Michel Vorm) have contributed greatly to the club's league position so far this year.

I'll mention two other clubs: first, Everton. The Blues are an outlier in the lower right hand corner, suggesting that they have managed to prevent their opponents from generating too many chances. In fact, Everton lead the league in allowing the fewest number of shots on goal (at 9.6). But curiously, the chances opponents did create stood a better than average chance of going in (pun intended). On this dimension of defensive performance, Tim Howard & Co. are 4th from bottom in the league. The other team that's worth taking a look at is Sunderland - as on offensive performance, the Black Cats haven't been an outlier at all. They find themselves right smack in the middle of the pack.

So, what to do in the transfer market? Perhaps one way to look at the information above is to consider what clubs should not do. Consider Blackburn. Given their performance so far, one thing they should not do is sell Chris Samba - unless they have resigned themselves to playing in the Championship next year. If not, they would do well to consider buying other help in the back, or perhaps in goal (my sense is that Paul Robinson hasn't been playing as well as Rovers need him to). Wigan, too, need all the help they can get, both in preventing opponents' shot creation - so perhaps help in defensive midfield - and the back.

City look like they don't need any help - they look outstanding, statistically speaking, and should continue to do what they've been doing - until you consider that they won't have the Toure brothers and Vincent Kompany available for some time. This may tempt them to spend some of the money a Tevez sale may generate to sign defensive reinforcements.

What about the rest of the clubs? They implications of the data are less clear here, if you ask me. Some of the performance may be due to tactics or coaching, rather than ability, so I would be more hesitant to suggest buying new players to deal with a bad defensive goal to shot ratio (though good goalkeeping has never hurt anyone). And if you are a selling club, make sure you ask for a premium if you're selling to the teams in the upper right quadrant.

Monday, January 9, 2012

Transfer Window Benchmarking I: Offensive Performance in the Premier League

Now that the transfer window is open, I thought it was time to take a quick look at how Premier League clubs have been performing on various dimensions. Let's start with offense for today. Which clubs have been doing exceptionally well, and which ones seem to need some help, perhaps by finding a player or two?

Below is a graph of number of shots created by the goals/shots ratio so far this season (through January 4). Recall that teams in the upper right hand corner both created lots of chances and managed to convert them to goals very efficiently. In contrast, teams in the lower left hand corner neither created shots nor scored very efficiently off the chances they did have (the green lines denote the league median - 50% above and below).

With these very simple numbers in hand, it is not very difficult to figure out why some teams have been over- and under-performing the rest of the league offensively.

Manchester City lead the pack on offensive production - the Citizens created more shots than anyone else, and their shots were more likely to find the back of the net than anyone else's. Contrast that with Liverpool FC: Suarez & Co. produced as many shots as Chelsea or Tottenham, but they were literally half as efficient as Manchester City, and roughly a third less efficient than other top teams like Arsenal, Tottenham, or Chelsea. In fact, Liverpool were so bad in front of goal this year, there was only one team that performed worse (Fulham). In fact, both Merseyside clubs struggled when it came to converting chances to goals.

Very curiously, Blackburn's goals to shots ratio was second in the league - almost as good as Manchester City's. That's a remarkable fact, if you ask me, and testament to the fact that Rovers' Achilles heel does not appear to be in taking chances when they present themselves. Instead, Rovers aren't very good at creating them in the first place (and this obviously says nothing about their defensive prowess).

One other club stands out by not standing out. While Sunderland did not have a great first half of the season and fired their manager, they were squarely in the middle of the pack on offensive production.

So, what should clubs take away from these basic statistics?

To survive, Blackburn need to find a way to create more shots (as do West Brom, Bolton, Swansea, Aston Villa, and Stoke). In contrast, to crack the top 5, Liverpool need to find a way to put them away (as do Fulham, Everton, QPR, Wigan, and West Brom). Finishers should be able to command a premium.

And if they want to contend with the clubs from Manchester, the aspiring London teams (Tottenham, Chelsea, and Arsenal) need to improve their finishing or find players who can do it for them (or they need to hope for the Manchester clubs to regress back to the mean).