Field Position And Goal Expectation In Football
How does field position impact upon the expectation of a goal being scored? Today on the blog Mark Taylor takes a look by comparing the final season of Robin van Persie at Arsenal and his first season at Manchester United.
There is no doubt that we are currently seeing an explosion of statistically based football analysis that will help to illuminate and enlighten how we view every aspect of the game. For far too long goals has been the only readily available statistic to measure both team and individual player performance. We are now almost spoilt for choice as multiple amounts of granular information gradually becomes available, leading to more advanced football statistics beginning to find their way into the media.
Goal Expectation Based On Field Position
Inevitably, many of these newly collected numbers will still relate closely to the art of scoring or preventing goals from being scored and one of the most powerful new tools to emerge in recent months involves how likely a player is to score from any particular field position.
Goal expectation based on field position can immediately begin to add layers of detail to a player’s shooting and conversion statistics and quantify what our eyes already tell us about striking talent. It is already being featured by some of the mainstream media and will likely be the first of the new breed of statistics to gain a wider acceptance.
A typical shot from 12 yards out and central to the penalty area in open play is converted just under 20% of the time compared to nearly 80% for a penalty kick from the same spot. So already we can begin to see the effect of a striker having to cope with defenders, being required to control a pass and beat a keeper who is active rather than passively waiting on his goal line.
It is tempting to ascribe the increased conversion rates seen in outstanding players as being solely a product of their greater talent levels compared to an average Premiership striker. However, while individual talent is undoubtedly very important, team quality will also contribute to a striker’s goal scoring record above expectation, initially by providing clearer chances, even when controlling for field position and also by providing equally dangerous team mates, who also require the full attention of the defence.
An Analysis: Robin van Persie
Separating the team input from individual talent will prove difficult, but the recent high profile transfer of Robin van Persie from Arsenal to Manchester United does allow us to take a sneak preview into this next step in the process. Little work has been done on a player’s ageing profile in football, but extrapolating from similar sports when physical fitness and eye co-ordination are required, it would seem reasonable to assume that at 29, van Persie is around his peak. Certainly we should not expect a sudden, dramatic change in the levels of goal scoring ability that he has demonstrated over the last couple of completed seasons at The Emirates Stadium.
His final 2011/12 season with Arsenal was one of van Persie’s most successful from a fitness stand point. He failed to appear in just six of the Gunners’ matches, usually low profile cup matches or dead Champions League games and prior to his unfortunate coming together with a camera on Saturday, he has maintained that level of fitness at Old Trafford.
Therefore, the van Persie of 2011/12 should be very similar to the van Persie currently heading the Premiership scoring charts for his new employers. Any substantial difference in such personal statistics as shot conversion will likely have a lot to do with the two different sides he has represented over the one and three quarters of a season. In short, we may be able to use van Persie as a standard by which we can measure the different quality of the chances created for him at Arsenal and subsequently at Manchester United.
Robin van Persie’s Chance Conversion Statistics Since 2011
|Club||Goal Attempts||Goal Expectancy||Actual Number of Goals|
|Man United 2012/2013||94||10||19|
Robin van Persie had 173 goal attempts in his final season at Arsenal, judged on the position of each attempt, an average Premiership player, be he a recognised striker or a defender in an unaccustomed advanced role, would have expected to score 20 goals from those opportunities. Unsurprisingly, for a striker of van Persie’s quality, he scored 50% more than the average expectation. In addition to this impressive 30 goal haul, the Dutchman was on the pitch while virtually all of Arsenal’s 74 league goals were scored and therefore, he accounted for 41% of their goals.
In his first season with the current runaway leaders of the Premiership , he has scored 19 times from his 94 attempts. These chances had a cumulative, average goal expectancy of just 10 goals. As you would expect he is still performing above the average, but by a much larger amount than during his last Arsenal campaign and he is scoring at almost double the expected rate for a par Premiership player.
If we reasonably assume that nothing has really changed to make van Persie a substantially better player and accept that 94 attempts is a large enough sample size to be largely indicative of his true scoring ability for United, then the most likely reason for his improvement is the quality of the chances he has been presented with.
United have striking quality a plenty, occasionally operating with van Persie as part of a three forward attack. As a consequence he has only scored 33% of United’s goals which have been scored while he is on the pitch compared to his more impressive percentage at Arsenal. This more equal division of the goal scoring spoils means that van Persie is but one of multiple penalty area threats and he is likely to find slightly more space as part of the Manchester United forward line compared to his last days as a Gunner.
We can further speculate that the quality of the final ball may also be superior at United in comparison to 2011/12 at Arsenal. In short, an open play shot from the penalty spot may be a slightly easier proposition for van Persie this year than it was last.
Even great goal scorers find it easier playing with better colleagues and van Persie’s exceptional, career high conversion rate may be indicative of the universally accepted superiority of the current Manchester United side over the Arsenal side of last season.
Read more of Mark's work on his The Power Of Goals blog
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