Saturday, 13 April 2013

In Defence Of Corner Kicks.

The fluid nature of football makes it tempting to concentrate on the occasions where the whistle is blown, the play stops and the game is restarted with a set play. A penalty kick provides a side with an excellent opportunity to register a goal and therefore they have received the lion's share of the attention, but the spotlight is increasingly falling on corner kicks, particularly their value in terms of scoring likelihood.

Many have pointed out the low rate of conversion from corner kicks. Most recently Tijs Rokers wrote in the excellent, data driven blog "The Sixteen" about the three percent goal success rate from such set pieces in the Dutch league, a figure that is consistent with scoring records in the Premiership. One goal every 30+ corners, where teams rarely average much more than 5 or 6 corner per game can therefore make corners appear almost insignificant incidents, even in such a low scoring sport such as football. Increasingly, corners are becoming unloved and even the very act of launching the ball into a crowded and well defended box is being portrayed as an outdated and inefficient throwback.

So let us try to redress the balance.

The Futility of Corners ?
Corner data is still relatively patchy, but the two most usually quoted numbers are success rate, denoted by first contact by an attacking player and conversion rate. Unfortunately, despite it's enticing description, the former is completely uncorrelated to the latter. Here's a (painful) example. Villa had two corners last week at Stoke's Britannia Stadium. The first was deemed "successful", but didn't result in a goal and the second in the 85th minute of a stalemated relegation scrap was "unsuccessful" because a Stoke defender got first contact and cleared the ball from the near post. It was further scooped ten yards beyond the edge of the area. At which point Lowton smacked a dipping volley just under Begovic's bar. An unsuccessful corner by one definition which resulted in the winning goal from a corner by another. A wider plot of corner conversion rates against the percentage of first contact by attacking players confirms that Lowton's enigma is far from unusual.

Therefore, any attempt to extend the definition of a successful corner beyond the raw conversion rate is likely to prove fruitless using the current, limited and confusingly defined data.

To rehabilitate corners as an attacking threat we need to reexamine their apparently underwhelming 3% conversion rates. When comparing the effectiveness of different approaches to goalscoring it is essential that we are comparing like with like. Corners are merely attempted assists which sometimes result in a goal attempt and sometimes do not. Understandably, the obvious nature of a set piece has led to corners which don't result in a goal or even an attempt, appearing prominently on the ledger which records corner efficiency.

The yardstick of chances created from open play, to which corners are often unfavourably compared isn't similarly tainted. Goal attempts from open play appear to have higher success rates than goal scoring rates from corners. But the comparison is flawed because attacking moves which break down before a shot is attempted (the equivalent of a corner which is successfully cleared) are very rarely included in the analysis of chance creation from open play. To do so would require a thorough interrogation of play by play data from every Premiership game, along with video analysis.

In short, a two on one attacking situation which breaks down and is cleared by the lone defender is merely logged alongside numerous other unsuccessful final third passes, it is unlikely to be flagged as a failure of chance creation from open play. Whereas when a defence successfully clears a corner, it is marked down as a set piece failure. Football analysis is as much about trying to accurately record what didn't happen as it is about recording what did occur and in this regard corners and other set pieces are victims of their own conspicuousness.

If we want to damn corners because of a 3% conversion rate,we are selectively cherry picking our data. Ideally, on the negative side, we must also include the occasional threat of conceding on the counter, along with the likelihood that possession is going to be lost. On the plus side, we should include the likelihood that the defence may only temporarily relive the pressure by clearing the ball up field and may not totally eliminate the danger by regaining a full, controlled possession.

And we also need to perform the same reckoning for supposedly superior alternative strategies and include the less readily available turnovers and partial loss of possession and even counter attack goals which occur for example in open play. Only then can we start to fairly compare corners as precursors to a chance against their open play equivalent.

Set plays may still prove less efficient than other strategies, but the importance of having a mixed strategy is evident in other sports. NFL sides are rarely equally proficient at moving the ball on the ground and through the air, but the need for an opponent to prepare for both can see the existence of a team's weaker discipline aid the enactment of it's strength.

In football, a less nimble central defender may be exposed in a open play ground duel, but his presence in a side may relate to the need to defend half a dozen corners and a similar number of other set play crosses. One dimensional teams, even sometimes the very best, are often easier to frustrate and even occasionally defeat. Barcelona may struggle to implement their brand of possession based football when deprived of certain outlandishly talented players. Many cite the example of Spain as a successful, yet flawed one dimensional team.

Proportionally, some teams also rely more on set plays than on chances taken from open play. It is hard to imagine Stoke surviving in the Premiership for as long as they have done without the ability to "score off a corner". Corners, even before we begin to treat them on a level analytical playing field, are often essential elements for less talented sides, where producing numerous, higher conversion, open play chances may prove difficult for their overall quality of playing staff.

Corners are individual, discrete events, but in determining their worth we should take care not to fully remove them from the fluid game that is football.

1 comment:

  1. the most difficult part of the football game when you have to defence on the corner kicks