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Arsenal failed Premier League title bid partially explained by expected goals

For all the sound and fury of this year's Premier League season, the result has been largely the same for Arsenal. Yet again the Gunners look set to cruise to a third-place finish, albeit with slim chances of both second and fourth still alive, after spending a large portion of the year flirting with making a title run. What's different of course is that rather than the usual group of Chelsea, Manchester City and Manchester United finishing above them, this year it's Leicester City and, most unforgivably in North London, Tottenham Hotspur.

It was perhaps understandable when Arsenal finished behind some mixture of the only three teams in the Premier League that had more resources at their disposal than Arsene Wenger's club. But when all three of those rich opponents blow themselves up in one way or another in the same season and Arsenal still can't seize the opportunity, then more answers are needed.

This year, the answers Arsenal and Wenger seem to be providing come in the form of expected goals. It's a relatively new statistic, at least in the mainstream, but it's one that Wenger himself has mentioned several times over the course of the season. It's also one that as analytics becomes ever more ingrained in the fabric of club management, is at least available as a tool for most clubs to consult.

Expected goals is simply a formalisation of a conversation that soccer watchers have been having for generations. It's a measurement of the quality of the chances a team creates and gives up. Generally expected-goal measurements take into account things like where a shot was taken from, whether it was a header, the kind of pass that assisted the shot and then a host of more complicated factors designed to measure the degree of defensive pressure on the shot. These include things like the speed of the attack and whether a shot followed a successful dribble -- things of that nature.

Much like pasta sauce, everybody's recipe for calculating expected goals is a little different, but the end products are similar, though not identical. So, Arsenal's in-house analytics teams probably have numbers that are slightly different than ESPN Stats & Info's.

Olivier Giroud
Olivier Giroud and Arsenal's attack have struggled this season, falling short of the club's expected-goals projection.

In general, though, the measurement is quite accurate over time. And its power is in how it reveals that given enough shots, even the best and worst finishers in the game can't get very far away from the amount of goals their chances dictate they should score. The best goal scorers in the game get that way not by finishing phenomenally difficult shots, but rather by creating more easy shots than anybody else. Hot and cold streaks come and go, but creating the best chances, and keeping opponents from doing the same, is forever.

This year, the general consensus is that Arsenal have been very, very unlucky. According to ESPN Stats & Info, Arsenal have scored a whopping 10 fewer goals than expected. That's the biggest gap in the league, and it's not like it's mitigated on the other side of the ball where they've conceded, unremarkably, slightly less than two goals fewer than expected. They've been the gang who can't shoot straight.

While it might be easy to make fun of the likes of Theo Walcott, Olivier Giroud and Aaron Ramsey as habitual bottlers who can't put the ball in the net, we have years of data that show that it's not particularly true. Even players with reputations for missing chances don't miss them like this for long stretches of time, a fact that is borne out in Arsenal's history. Last season, based on their chances, expected goals projected slightly more than 72 goals for Arsenal; they scored 71. The year before, it projected 61; Arsenal scored 68.

Clearly, the explanation that Arsenal players aren't good enough at finishing their chances doesn't stand up to historical scrutiny. The same players certainly have been in past seasons. That doesn't necessarily prove that Arsenal have been unlucky, either. Given the relative newness of expected goals, it's certainly possible that the measurement is missing something about Arsenal's year.

Maybe Arsenal's relentless emphasis on high-quality shots was figured out by defenses this season, making their shots harder in actuality than they appear in the metric. Maybe the particular combinations of players that Wenger trotted onto the field in some ways exaggerated their worst attributes while muting their better ones. Expected goals is a good and useful tool for analysis, but that doesn't make it the end point of analysis.

Just because Arsenal's attacking performance this year might have simply been hamstrung by bad luck doesn't mean the team should ignore the possibility that other factors -- factors in their control but perhaps missed by an expected-goals measurement -- might have contributed to it. And even if there are no other factors, even if it's simply pure gosh-darn, honest-to-goodness random chance that they missed all those shots, Arsenal's postseason analysis still shouldn't end there.

On Feb. 14, Arsenal came from behind to defeat Leicester City 2-1 in a thrilling match to draw even with Tottenham, two points off the eventual champions. With 12 games left in the season, it seemed like a three-team race, and one that Arsenal were the most equipped to win. Since that point, Arsenal's performance has been downright mediocre.

Their goal tally of 20 actually flatters their expected-goal total that is between 16 and 17, only the seventh best in the league over those 11 games. And in reverse, they've been somewhat unlucky defensively to concede 13 goals while their expected goals tally was only slightly above 10, the second best in the Premier League. Since that dramatic win, they've been a very good defensive side combined with a Europa League-level attack. That's probably good enough to finish third, but certainly not the stuff that Premier League title-winning challenges are built on.

Even assuming expected goals is absolutely spot-on this season, what it's saying is that Arsenal were very unlucky early in the year, but roughly where they should've been down the stretch. Chalking up Arsenal's season to bad luck is, in effect, saying that if Arsenal hadn't gotten unlucky early in the season they'd have been able to win the title despite not playing at a Premier League-winning level for the last third of the season.

Using expected goals to chalk up Arsenal's failings this year to luck is doing it exactly backwards. It's elevating the things they couldn't control, like consistent finishing, during the first two thirds of the season over the things they could, like not playing well enough over the last third.

The metric of expected goals is an extremely useful tool. As part of a decision-making process, it can help teams focus on what they can control while not getting bogged down in the things they can't. But even the best tools don't work if you hold them upside down.

Mike L. Goodman is a Washington, D.C.-based soccer writer and analyst covering European soccer, the U.S. Men's National Team and more. Follow him on Twitter @TheM_L_G.

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