Monday 30 September 2013

Are Arsenal's Goal Scorers Good Enough For A Title Tilt?

It is nearly a decade since Arsenal managed to wrest  the Premiership title away from the likes of the two Manchester clubs or their near rivals, Chelsea. So despite a inauspicious start, culminating in a home defeat to Aston Villa that led to knee-jerk calls for Wenger to go, they now find themselves handily placed atop the six game table. A run of five consecutive wins has sent Arsenal four points clear of Chelsea, five clear of Manchester City and eight points ahead of the most recent Manchester side to lift the title.

Goal scoring has been at the forefront of Arsenal's rise back to the top and although it is obviously early days, they are currently on pace to score 80+ goals. That's also the average seasonal goal scoring total achieved by the champions over the the last decade. Sides finishing in fourth average 67 goals a season, rising to 70 for third 76 for second. Simplistically, a side finishing fourth, Arsenal's most common finishing spot since their last title in 2003/04, would ideally be looking to improve their goal scoring by around 23% to achieve a more typical value of Champions.

Defensively, Arsenal has allowed just over a goal a game, on pace for 38+ goals over the season. Typically, fourth placed sides allow around a goal a game over the season, compared to 26 for the Champions. That represents a defensive improvement of nearly 30% between the average defensive performance of the fourth placed side to attain the average record of the Champions.

So increasing goals scored may be the easier half of the deal for a top four side to aspire to rise to the top of the pile.

These crude, early season projections hint at an attack that may have reached a level worthy of a championship tilt, but 13 scoring events hardly inspires confidence in any prediction. However, shot totals do increase the body of evidence. This campaign, Arsenal has made 87 attempts on goal, 15 of which were headers and 72 shots, in scoring their 13 goals. 27 efforts have been blocked and 25 have been off target. So the raw numbers are impressive, if likely unsustainable.

Shot location models can be used to estimate an overall goal expectation for an average team presented with all of Arsenal's attempts so far this season and Arsenal's actual goal tally can then be used to see how effective the Gunners have been in their first six games of 2013/14. A record of 13 goals, when an average side would likely only score 6.5 goals is undoubtedly impressive, as are 35 shots on target against an average expectation of around 26.

However, such favourable comparisons are hardly unexpected for a regular top four side, such as Arsenal over the last decade and the yardstick of a fictitious average side also provides an opaque standard. Therefore, to create a more relevant conclusion from the shooting data, I took all of Arsenal's shots from a recent season, 2010/11, ran a regression using those actual outcomes to see how likely that earlier side were to score from any shooting location on the field and then inputted the shot co-ordinates so far for Arsenal from 2013/14.

By creating a baseline model based around Arsenal (2010/11), a side that scored 72 goals in finishing fourth, we can see how likely it is that a side of that quality might score the 13 goals and hit the target 35 times from the 87 opportunities created by the Arsenal 2013/14 vintage.

                     Likely Goal and Accuracy Outcomes for Arsenal's 87 Attempts in 2013/14.

The 2010/11 team of van Persie, Arshavin, Nasri, Chamakh, Fabregas and Walcott, had they been presented with the 87 2013/14 chances, would most likely score between 7 and 8 goals. The distribution from simulating thousands of 2013/14 seasons, using shot co-ordinates from the current campaign, but the conversion and accuracy expectation of the 2010/11 side, indicates that such a combination would score the present Arsenal's total of 13 goals around 2.8% of the time. Just over 5% of the time, 13 or more goals would be the result. Also, Arsenal's 2010/11 side would possibly hit the target on the 35 occasions achieved already this season, 2% of the time. Equaling or exceeding this total in 5% of the trials.

Once again, this time when matched against an earlier incarnation of themselves, rather than an average baseline, the present Arsenal team appear to be at least worthy of their current position.

These simulations, which (imperfectly) compare the attacking component of the Arsenal side that finished 4th three seasons ago with 72 goals and 68 points, to the current achievements of Ozil, Giroud, Ramsey and Podolski, can be interpreted variously.

For instance, the pessimist may point out that there appears to be a 5% chance that the 4th placed also-rans from 2010/11 could have produced an as good, if not better record than the one posted in the six matches during August and September by Wenger's current team. So the first six games may just be a lucky, short term streak from a side with similar offensive capabilities to the one that fell short two completed seasons ago.

Or alternatively, the optimistic Arsenal supporter may consider the present record of 13 goals so far to the right of the likely range of outcomes that could have occurred if the opportunities had fallen to the 2010/11 side, that it is reasonable to conclude that Wenger's has a more potent strike force at his disposal than he had when van Persie was the focus.

Shot models can create numerous scenarios, but the subsequent interpretation can be much more subjective.

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