Friday 30 November 2012

Defending Your Corner. The Anatomy of a Stoke Goal.

Unlocking the secrets of a football match can be made slightly easier by concentrating on the important actions, such as shots and saves for individual players and set pieces, including free kicks and corners for teams. Set plays by their premeditated nature offer a relatively consistent level of defensive and attacking opportunity and by looking at the effectiveness of teams against a variety of different opponents we may be able to start to characterize what constitutes good set play defence and attack.

Manchester City demonstrated how important turning corners into goals is to a team's season. Generally, in the 15 Premiership goals which they scored in the immediate aftermath of a corner kick over the season as a whole and particularly, with the vitally important late season winner against title rivals, United and the 92nd minutes equaliser at the climax of the title race at home to QPR.

The champions also greatly improved their scoring rate from corner kicks compared to the previous year, perhaps indicating that there is profit to be had from identifying and implementing a successful set piece strategy.

One team which has long understood the importance of dealing with corner kicks at both ends of the field is Stoke City. Their opening goal against West Ham was clearly the product of work put in on the training field, with Gary Neville describing Walters' strike as "one of the goals of the season". Others preferred to highlight the perceived illegality which preceded the strike. Blocking opponents to provide clear space for a team mate isn't restricted to football, sending dummy runners in front of the intended ball receiver is now well establish in rugby, but physically preventing attackers from getting a clear run in football has even survived the introduction of extra officials in the European competitions. In short referees have set a line in the sand for acceptable behaviour at corner kicks which may not be fully reflected in other areas of the pitch and all teams exploit that leeway to the maximum of their ability.

Measuring corner kick success does require a certain degree of subjectivity. For example, six of Manchester City's set play goals came directly from first headed contact with the corner and three other from assists. Other scores came from extended play following a short corner or a ball deliberately played to a central area just outside the edge of the penalty box. Therefore it is sensible to divide corners into situations, such as short corners where possession is guaranteed and occasions where the ball is played directly into the box where the possession pay off is less, but if first contact is made with the cross, it is in a more threatening area.

The availability of x, y coordinates for match events has allowed us to chart match incidents, attempt to define success and quantify success rate for different areas of the pitch. In 2011/12 Stoke won over 150 corner kicks  in the EPL. As you'd expect for a side blessed with such an aerial threat very few kicks were played short or to the edge of the box. The average position for the targeted area was just north of the six yard line and around a foot west of the penalty spot in the direction of the near post.

In short, Stoke were aiming for the area in the box where a clear header is increasingly likely to produce a goal. As this post shows, the further you get from the goal, the less likely you are to score with a header compared to a shot, but inside the six yard box the situation is reversed an headers are an extremely potent option.

In this initial analysis, I've recorded all of Stoke's corner kicks and used a Stoke player making first contact with the cross as a broad definition of a successful kick. As a comparison I've included the "success" record for all the other EPL teams when launching corners into the Stoke box. We are looking at a combination of Stoke's corner taking ability matched to their opponents ability to defend the ball and vice versa.

I'm going to try to avoid overuse of figures in this post, but I will use them to verify my intuition that Stoke have worked very hard at defending and attacking corners over the last two completed seasons. The line of the six yard box appears to be the crucial area where header start to lose potency. Corners are also likely to see the six yard box more heavily defended than is the case in open play, so while conversion rates are likely very high deep into the six yard box, the likelihood that an attacking player will get the first touch quickly falls away to around 3% or less as he nears the goal line in the case of corners.

The starkest comparison between Stoke defending and attacking corners is in their ability to get the first touch to corners hit centrally to the six yard line. They have around a 1 in 5 chance of beating the defence to the ball, whilst restricting their opponents to barely half that success rate.

Stoke's Opening Goal from a Corner against Swansea.

Although the goal mouth action following a corner appears very haphazard, more of the initial movement and delivery is well rehearsed. Stoke's attacking and defensive ratios may be unsustainably high but as a team, they are undeniably well versed in creating and denying space at corners.

The above photo shows Stoke's opening goal at home to Swansea, this season. Glenn Whelan has already executed the first part of a successful corner by accurately hitting an inswinging corner at pace, centrally to the edge of the six yard box. The pace of the cross ensures that the Swansea keeper is reluctant to leave his line, but just to be sure, Steven N'Zonzi (1) takes just enough of his ground to make staying put appear a better option. N'Zonzi's height also enables him to hinder Vorm's ability to clearly see the action as it unfolds in front of him.

Huth (2) is just one of Stoke's incoming runners, Walters is off camera to the left and Huth's imposing size accounts for two Swans defenders. Shawcross has already ran corner side of the near post to draw another defender out of the six yard box. Despite his heading prowess, he has been used here as a decoy runner, or as an insurance should the corner be under hit.

The decisive action has occurred far post. Adam (3) is partly there to act as a blocker for target Crouch (4). Crouch has run his marker in towards the far post before peeling back into the middle of the box where the ball is going to be delivered. His marker has anticipated a far post run, but now finds himself blocked off by Adam, who merely has to stand his ground to give Crouch an unmarked free header, which he duly dispatches. N'Zonzi is ready to become active should the ball be blocked on the line.

It's great when a plan comes together as it did here and against West Ham as illustrated by Neville and each of the seven Stoke players had an important part to play in freeing Crouch for a clear header.

Stoke Defend a Swansea Corner....

....and another.

Defensively the Stoke players are intent on staying close to their opponents. Shawcross and Wilson in the first shot and Shawcross and Cameron in the second are engaging their marked opponents to such an extent that challenging for the  ball becomes almost secondary. Walters and Wilson in the second photo are also physically imposing themselves on the two most likely recipients of the Swansea cross. In short, physicality, denying strikers the freedom to make runs and a 6'5" keeper goes some way to explaining Stoke's ability to prevent their opponents from enjoying the same amount of successful first contact with corner kicks which they themselves enjoy.

These are idealized examples of Stoke City dealing with corners at both ends of the pitch, but the stats clearly indicate that they are likely to be above average in both abilities. Their opponents have acknowledged the futility of attacking the heart of Stoke's six yard box directly, by taking around 20% of corners short. Stoke, by contrast took less than 4% of their corners short last term.

Pulis has long relied on a mean defence to maximize his team's dearth of goal scoring and goalsoring from corner kicks regularly account for a significant proportion of their goals. Scoring rates of a goal a game aren't uncommon for Pulis led sides and this season is no exception and 15% of the strikes have come directly from corners.

The numbers can help to identify trends in team quality, but often game footage can then add the meat to the story. Stoke are adept at creating and denying space and the hard work, often on the edge of legality rarely appears explicitly in the currently recorded data.

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