Monday 11 May 2015

Middlesbrough's £10 Million Corner Kick.

Jose Mourinho isn’t a fan of corners, apparently. So he no doubt took the opportunity of such a 94th minute set piece at Griffin Park to slip away and beat the traffic following Middlesbrough’s first leg Championship play-off game with hosts Brentford.

Middlesbrough boss, Aitor Karanka, perhaps takes a more positive view of the much maligned corner kick than his friend, Mourinho and he was rewarded on Friday night with an injury time, deflected winner from Spanish defender Fernando Amorebieta.

The value of a corner kick is still debated, but for this particular effort we can quantify it in plain GBP. Prior to the injury time kick, Middlesbrough had around a 65% chance of making to the play-off final, reputable now worth around £130 million, for which they will be around a coin toss to reach the Premier League.

After the late winner, they’ve advanced their chances to round 82%. So in virtual, probabilistic currency, the corner, or more accurately the goal from the corner, has increased the value of Middlesbrough’s chips by around £10million.

Of course the ultimate result is an all or nothing outcome, with Brentford and either Norwich or Ipswich still very much interested parties.

More generally, corners result in much less extravagant potential swings in fortune. To take 2012/13 as a typical Premier League season, teams scored an average of 7 goals in the season from corners, compared to 46 from all other means. 

So goals from corners accounted for 13% of all goals scored.

Averages inevitably hide the extremes, only 2% of Newcastle’s goals were from a corner, followed by 6% of Arsenal’s, while Stoke scored 8 such goals and that made up nearly a quarter of their total scores.

Execution also appeared to vary, Arsenal needed to take 260 corners to score precisely half the total goals scored by Stoke from almost exactly 100 fewer set pieces. The Gunners also fashioned just 61 goal attempts from their 260 corners, again compared to 60 by Stoke from only 163 flag kicks.

The style of Stoke, pre Hughes, bore little resemblance to most other Premier League sides, especially Arsenal, but we should still entertain the possibility that the spread of chance creation and goal scoring from corners, seen at its most raw between these two rivals, may be simply due to random chance, rather than differing levels of talent or intent.

Overall 3.2% of corners resulted in a goal in 2012/13, but as we’ve seen there were extremes. Newcastle scored from just 0.5% of flag kicks, Arsenal, 1.5%, Spurs and Swansea, around 2%, climbing to nearly 7% for Manchester United, 5.5% for Wigan (who won the FA Cup with a last minute goal from a corner) and 5% for WBA, Chelsea, and Stoke.

Swansea take a corner.....Don't hold your breath.
This spread of conversion rates does suggest we are seeing something in addition to random variation. And it is repeated if we further look at the rate at which teams muster chances from corners. Arsenal fared the worst, creating an attempt from 20% of kicks and WHU were best with a 35% rate of diverting the ball goal-wards.

Shot models also suggest that a typical team would have an average 12.2% chance of converting each opportunity created by Stoke from corners in 2012/13, but just a 9% chance from each of those fashioned by Arsenal.

It is hardly ground breaking, but the evidence suggests that in 2012/13, Stoke were better at creating better and more plentiful goal scoring chances from corner kicks than were Arsenal and that graduation of skills probably existed in the remainder of the Premier League.

Unsurprisingly, the reverse is true of open play. 

There is no comparable precursor to open play chances as there is for opportunities made corners, final third possessions would probably come closest if it was readily available. The efficiency with which final third incursions are turned into open play goals may give a fairer comparison for corners to be judged against.

On this occasion, Arsenal beat Stoke hollow. They created 474 open play chances, from positions which would give an average side an 11% chance of scoring, compared to the Potters’ 236 open play attempts, each with an average generic 9% success rate.

So, in the grand scheme of an entire season, corners, as a means to create chances and ultimately score goals were a big deal to Stoke.  The Potters scored a quarter of their goals from this method and they were among the best in the league in terms of creation and conversion rates. A third of the Potters’ 25 best scoring opportunities were also made from corners.So they were a rich source of big chances during the Pulis swansong.

Sides which appeared to have both a talent to over perform against the average from corners in 2012/13 and gained the largest proportion of their total goals from such a source, included Wigan, who were ranked 2nd in over performance and 3rd in terms of goals from corners as a percentage of total goals. They were followed by Chelsea, Manchester United, Sunderland and Stoke.

Sides for whom corner kicks and their outcomes were largely an irrelevance, included Arsenal, Newcastle, Spurs and Swansea.

Soccer is a low scoring sport and even at base rate conversion levels for corners, the resulting goals from an average of 11 events per match account for 13% of a game’s total goals scored and when a side, such as Stoke can increase these baseline numbers, the importance of corners to them increases.

Crudely removing Stoke’s scoring from corners in 2012/13 leaves them marooned on 36 points, the same as the final relegation spot, rather than safe in 13th spot.

Not all corners by circumstance produce £10 million shifts in fortune, but whether they are the icing on the cake, as in the case of Manchester United in 2012/13 or a means to survive, as in Stoke’s case, they are important footballing events. 

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