Friday, July 29, 2011

Premier League Sharpshooters in 2010/11: Blues Shot The Most And The Least, While Spurs Shot Best

It's that time of year again when I start going through my data from last year to make sure everything is up to date and accurate before the new season begins. In the (tedious) process of coding and cleaning data sets, I try to have a little fun and benchmark a couple of things for the upcoming campaign. So just for kicks, here are the total numbers of shots (total and accurate) taken in the Premier League last year for each team. Below these two charts, there's also a graph that reports the accuracy ratio - the percentage of total shots on goal that was accurate - for each team, indicating a team's efficiency at producing high quality shots.

As a baseline, the total number of shots taken in the Premier League last year was almost 9,500 (9,449 to be precise), while the number on target was 5,173. The Blues of Chelsea and Birmingham shot the most and least, while Spurs were most efficient. A couple of surprises: WBA's shot frequency and Chelsea's profligacy. Feel free to point out other patterns (or mistakes) in the data.

Over the next few weeks, I'll provide more summary data on last season for the major leagues. Stay tuned.

Wednesday, July 27, 2011

Goals From Fast Breaks: The 2010/11 Premier League Rankings

Although some of this information is elsewhere on this blog in other form, by popular demand in response to the earlier post, here are the total number of (Guardian Chalkboards/Opta defined) goals from fast breaks (first graph), as well as the ratio of fast break goals to all goals (second graph) for last season (2010/11). To orient yourself, recall that teams scored about .08 goals from fast breaks per match, and the average team scored about 6% of all goals from fast breaks - though in both categories there was lots of variation, as you can see.

Aside from the curious outlier Wigan, teams like West Brom and Manchester United managed to score almost 10% of their goals from fast breaks. In contrast, not even 1% of Newcastle's came from this source.

See any other interesting patterns? Enjoy!

Tuesday, July 26, 2011

Which Goals Matter? The High Value of Transition Play in the Premier League

While some goals are certainly more beautiful than others, do some actually matter more than others? I've been trying get a bead on this question in part by comparing the relative value of goals created in different ways. My earlier analysis of Guardian Chalkboard/Opta data for the Premier League from the 2010/11 season suggested that open play goals had a stronger statistical connection with points or wins than set piece goals did (The Guardian defined set piece goals as resulting from penalties, free kicks, and corners). The correlation between open play goals and wins/points was about twice as strong as the correlation between set piece goals and match outcomes. So both contributed positively to points and wins, but the data also indicated that open play goals had a significantly stronger connection with match outcomes.

The natural next question is why. Part of the answer seems to be statistical and lies in the distribution of the data. Curiously, the results suggested that the odds of winning the match are better with 0 set piece goals than with 0 open play goals - but how can you have positive odds of winning with 0 goals of any kind, you might ask. The reason for this simply has to do with the fact that there are many more open play goals than goals from set pieces, so in every match with zero set piece goals, the chance of there being at least one open play goal are still very good. In fact, considering all matches played by teams last year (in the EPL, that's always 760 matches, since we have 20 teams playing 38 matches per season), there were 560 matches with 0 goals from set pieces; and of the 560 matches with 0 set piece goals, there were 358 that had at least 1 goal from open play).

So let's try to account for this. For starters, we want to isolate the true, independent, value of a goal of a certain type (open play v. set piece). One way to do that is by calculating how goals change the odds of winning if only one type of goal is being scored in a match. So for the fun of it, I took out my statistical magic wand, ran some regressions, and set each of the goal categories - open play and set piece goals - to zero while allowing the team to score with the other goal category. This allows me to simulate different scenarios, given the underlying patterns in the data. I then calculated the odds of winning the match when we score only from one type of goal (statistically speaking, that is). This tells us what the value of an open play goal is, assuming that there are no set piece goals in a match, and vice versa.

When we graph these results, we get the following picture of how scoring each of these types of goals changes the odds of winning, assuming there are no goals of another type in a match.

When no goals are scored of either type, the odds of winning are, well, zero, as the graph shows. What's more interesting, though, is that the line for open play goals is a bit steeper than for set pieces. There is only a small difference in how much each type of goal matters to the match outcome when it's the only goal a team scores in a match. But once you get to two or three, the odds of winning increase more rapidly with open play goals.

So far so good; but why would that be, I wondered? One possibility is that not all open play or set piece goals are created equal. In particular, as you may know, I have been wondering about the uselessness of corners and free kicks and the usefulness of fast breaks in football.

Thursday, July 21, 2011

Big Mo, Little Mo, Or No Mo? Evidence of Momentum in Football Matches

A couple of months ago, I made the point that football matches see more goals in the second than the first half. That is, the odds of either team scoring a goal increase over the course of the average match. I forgot about that fact until a few days ago, when I was talking to a friend about the hot hand phenomenon in basketball.

Now, mind you, the hot hand phenomenon has been thoroughly debunked, starting with the study by my colleague Tom Gilovich and collaborators over 25 years ago (there's also a nice summary of the hot hand phenomenon for interested readers in Moskowitz and Wertheim's Scorecasting). But the conversation did get me thinking a little more about momentum in football matches.

The fact that scoring increases over the course of a match that doesn't tell us whether teams' ability to score in the first half makes it more or less likely that they will score in the second half. In fact, you might think it could go either way: if the odds of scoring increase with every minute, then you might assume that teams that failed to score in the first half would become more likely to score in the second half (since they haven't yet made good on the overall statistical tendency). But alternatively, if you are a believer in the hot hand idea, you might think that teams that score early become more likely to score again. If teams get into a rhythm of playing (and then scoring), this would mean that we should be able to see something akin to a "hot foot" phenomenon (or perhaps momentum at the team level) in soccer.

To see if there is momentum in football, we would ideally like to have data for each goal's timing across the course of the match. I don't have these data handy at the moment, but perhaps the next best thing; namely, first and second half goal totals for each team and match. To make things systematic, I used as much data as I could quickly put together. So using match data for 5 seasons of the 4 biggest leagues in Europe (from 2005/06 - 2009/10), I wanted to see if the number of second half goals teams score go up, go down, or stay the same depending on how many goals they scored in the first half.

Keep in mind that the average team across the four leagues scores .58 goals per match in the first half and .74 goals in the second half. There is a slight bit of variation across the leagues, as the following graph shows. Overall, there was more scoring in the Bundesliga than in the other three leagues, but each league sees a difference of between .14 and .18 between the halves.

But back to hot footedness. If there is something to the momentum idea, then the number of second half goals should increase with the number of first half goals. But if not scoring early makes scoring later more likely, then we should see the reverse: fewer first half goals should be associated with more second half goals. And if it's all, well, humbug and logically flawed, then we should see random patterns across leagues. So here's what the data look like when we calculate the number of second half goals in a match by the number of first half goals a team managed to score in the same match. Judge for yourself.

Tuesday, July 19, 2011

Too Much Football: Is There A Connection Between Matches Played and Goals Per Game?

Over the past couple of weeks, I've been writing about league characteristics, including average goals per match and league balance. As we've been digging a little more into the data, Benjamin Leinwand and I have noticed a slightly curious pattern: goals per match seem to be correlated with the number of matches played in a season. We've all heard the common complaint that England's players aren't doing as well in international competitions as their performance in league play would suggest, with fatigue after a long season often cited as one of the factors. Could there be something to this?

So here's what we did: we took the goals data we collected for the six leagues we've been talking about (Bundesliga, EPL, Eredivisie, La Liga, Ligue 1, and Serie A) for the 1995-2010 period and calculated the average number of goals per match for seasons and leagues that saw 34 league matches and compared them to those that involved 38 league matches.

And lo and behold, averaged across the leagues and years, we see that there is a distinct difference between the two season/league formats: leagues where teams play 38 matches see 2.54 goals while leagues with 34 matches see 2.82. And that difference is highly significant, statistically speaking. So could this be behind some of the scoring differences we see across leagues?

Sunday, July 17, 2011

Shot Distance "Leaders" in the EPL: 2010/11 Data

If you're a regular reader of this blog, you probably think I've gone overboard with my Wigan obsession of late. And you're probably right. But I just can't resist the temptation to show one more picture of Wigan's inability (or unwillingness) to get anywhere near their opponents' goal. Courtesy of Albert Lacarda of ESPN's Stats & Information Group, here is a picture of average shot distance (sans penalties) for the entire 2010/11 season.

Not only did Wigan "lead" the league; but the entire group of "top" teams that didn't turn up very much in front of goal to shoot includes 2 of the 3 relegated teams (West Ham and Blackpool), 2 consistent strugglers in fear of relegation for much of the season (Wigan and West Brom), and one team that shouldn't be on this list (Tottenham).

The lesson: yes, you can survive the season even if you shoot from afar, but you probably shouldn't try.

Thursday, July 14, 2011

Football, Interrupted: Wasting Time in Men's and Women's Football

A few weeks ago, I wrote about how much football teams actually play. In the top professional leagues, actual playing time averages to between 61 and 65 minutes per match. In the post, I noted the obvious - namely that the clock can be your friend or your enemy, and that teams of course have the option to use it tactically.

Fast forward to the Women's World Cup being played in Germany, where Brazil's Erika the other day was heavily criticized for (possibly or actually) simulating an injury late in the match to delay the game in her team's favor in the match against the U.S. In part, the criticism seems to have been so heavy because it was a violation of an implicit norm in women's soccer. Turns out, women are significantly less likely to simulate injury than men, as researchers at the Technical University of Munich have found after studying 58 matches in detail. In their sample of matches, they found that play was typically interrupted for the same amount of time in both men's and women's matches. The interesting detail - and notable difference - was that women and men used interruptions differently. To quote from the report:

"The individual interruptions, though, are significantly longer in men’s football. Cheering a goal, for instance, takes almost a full minute with men, while women only cheer half as long. At 45 seconds, substitutions in men’s football take almost 10 seconds longer than in women’s football. Particularly striking are the differences in the duration of injury interruptions – the stronger sex remains on the ground 30 seconds longer. Overall, when women play, interruptions are more frequent, but the game generally resumes much faster than with men."

The data show that men celebrate longer, take longer to sub in and out, and hug the grass more, in particular when their team is ahead, as the report reveals. So if you ask me, the criticism of Erika was a little unfair; after all, she was doing what men do all the time. Talk about theatrics - and tactics, of course!

Wednesday, July 13, 2011

Tall = Good? Taller = Better? Height and Football

It wasn't all that long ago when playing midfield seemed to require more height than ever to crowd the center of the pitch. As a matter of fact, the average height of professional footballers has been increasing for a number of years now. The latest Professional Football Players Observatory report of the demographics of footballers in Europe reveals that players in the Czech Republic, Germany, and Denmark on average are around 1.83m tall - that's slightly over 6ft - while even players in "shorter" countries like Spain and France average slightly less than 5'11", as the following graph from the report shows. Mind you, each of these averages is significantly taller than the average male in these countries.

(c) 2011 Professional Football Players Observatory

In stark contrast, FC Barcelona seems to defy these general trends in professional football. While Iniesta, Xavi, and Messi are footballing giants, much has been made of the fact that Barcelona's midfield is one of the shortest around. What is more, they can probably look most guys in the Barca dressing room in the eyes. In the same report I cited above, Barcelona take the honors for shortest club in all of Europe (in terms of average height) at 177.38m - that's less than 5'10". So now, the latest fad seems to be what Germans like to call "Stehaufmaennchen" - or roly poly doll - a player whose center of gravity is low to the ground. 

So what's better? Tall or short?

Sunday, July 10, 2011

The Corner Kings: Blackpool's (Almost) Saving Grace

I've been looking for a positive way to say goodbye to Blackpool who were relegated after playing a single spirited and entertaining season in the Premier League. So here's my swan song for the Tangerines.

Corners are neither the most common nor the most efficient way to score. But as it turns out, Ian Holloway's men were the season's Corner Kings. Yes, Blackpool won the Premier League corners award. To see why, below are a couple of graphs of shots created by teams in the aftermath of a corner, as well as goals created from corner situations (all based on Guardian/Opta chalkboards data). They tell us several things.

First, teams were fairly similar across the board in the total number of shots they were able to generate from corner situations. The average was 2.1 per team and match, with most teams clustering right around the average. The only truly strong performer in terms of generating shots were Sunderland; the true underperformer were Wigan. So in terms of turning corners into opportunities, Blackpool were right there with the best teams in the league at over 2.1 shots produced from corners. But that's not all.

Fast forward a bit to producing goals from corner situations and we see that Blackpool and Newcastle led the league, as the graph below reveals.

Thursday, July 7, 2011

Do Open Play Goals Matter More? Data From the 2010/11 EPL Season

As you may know by now from some of the other analyses of goal creation I've done these last few weeks, most goals in the Premier League come from open play, while some types of set pieces (especially free kicks) only rarely yield goals. And, as I've noted, some teams create goals in very different ways from others - perhaps the most telling examples were Arsenal and Wigan last year.

But what these analyses don't tell us is which goals matter. Comparing Arsenal's and Wigan's fortunes last year, you may think that open play goals are associated with more wins. But why would, say, an open play goal be more valuable than a goal from a set piece for producing points and wins? A goal's a goal's a goal, right?! Actually, I have some ideas (more of a hunch, really) about why this might be, but before I even get to that, one question is whether there actually is a difference in the probability of wins or points earned, depending on the type of goal created.

Using the Guardian Chalkboard/Opta data I have collected for this last EPL season, for starters, I simply added up all goals from set pieces as defined by the Chalkboards (corners, penalties, and free kicks) and all goals from open play (open play, fast breaks).* As a first step I wanted to know what the correlation was between each of these types of goals created and points as well as wins. Recall that a correlation tells us whether there is a (linear) pattern in the data, where more of one thing (say, goals) goes hand in hand with more of another (positive correlation), or more of one goes with less of another (negative correlation).

So here are the correlation coefficients (Spearman's rho if you care) between number of goals of a certain variety on one hand and points and wins on the other for the 2010/11 season.