Corners at the World Cup
The 2014 World Cup has provided ample fuel for both watching pleasure and statistical analysis. The unusually open, goal laden start has given way to a more cautious, yet equally compelling knockout stage, highlighting the dangers of reading too much into too little sample size.
Goals from corner kicks have again illustrated the impact that even rare events have on tournaments where scoring is relatively scarce to begin with. 19 goals from 474 corner situations in the initial group stage has led to a slightly higher than usual conversion rate of 4%. But with each side scoring an average of just over 4 goals in total in their three qualifying matches, even these low conversion rates have dramatic effects upon qualification for the knockout stages.
14 teams scored at least once from a corner in the group games and 11 of those 14 progressed to the Round of 16, partly through this welcome scoring boost. All four sides in Group A scored at least once from a corner, so two teams were bound not to advance, making the overall progression rate for corner scoring teams even more impressive. Goals from corners contributed nearly a quarter of the total goals scored by these 14 sides.
The focus should be on how likely it is that a side, given an average number of corners, will score a particular number of goals from those corners. Using the more common 3% conversion rates from corners and applying them to the group format of Brazil 2014, there was around a 7% chance that a side would convert exactly two goals from corner kicks in their three group stage matches. Similarly, an individual side would score at least one goal from a corner in around 15% of their games and a match would see at least one such goal scored by either side 25% of the time.
These aren’t insignificant likelihoods, especially when we consider the goals that a side might also concede from a corner rather than merely concentrating on goals that they may score in this way, as is often the case in such studies.
In a competition such as a World Cup Finals consisting of 32 teams we should have expected between two or three teams to have scored exactly two goals from corners in the group stages and USA, Mexico and Colombia each obliged.
Uruguay turned a dwindling 15% chance of qualifying for the Round of 16 with 10 minutes of the group stage remaining into a near 90% probability by scoring from a corner against Italy and Brazil needed a similar goal to see off, first Chile in the initial knockout game and then Colombia in the quarter final. Surprise qualifiers, Mexico and USA also owed their progression partly to currently unloved, but finely executed goals from a corner kick.
Are corners worthless?
So goals from corners may come as a surprise, but in a sport where goals themselves are also scarce, they often have a major effect.
Corners are set plays within a fluid game and defining their effectiveness is often open to subjective opinion and teasing the transitions from one phase of play to another is difficult. Diego Godin’s emphatic first contact header for Uruguay against Italy was the definitive example of a goal scored from a corner delivery. But less clear cut was Liverpool’s equally dramatic last minute winner at Blackburn in 2012.
Agger flicked on a 40 yard punt from halfway and Carroll headed home a last minute winner, so the goal originated from a pass 50 yards from goal, but the defensive confusion in Blackburn’s defence and Liverpool’s temporary attacking set up comprising their two central defenders owed everything to the corner kick that had immediately preceded the goal.
A cut-off point may be required to designate whether or not a score originated from a corner situation, but defining a corner as the initial kick and three subsequent passes is merely a convenience for the data collector, rather than being based firmly in reality.
Corner kicks invariably disrupt a well ordered defence, with attackers temporarily pressed into performing unfamiliar defensive duties and necessitating the inclusion in the side of some players with aerial talents whom may be more exploitable on the ground in other phases of the match.
Mixed strategies are almost always preferable in the long term to a one dimensional approach, even extremely potent ones such as employed recently by Barcelona and Spain and the threat of having to defend half a dozen long corners during a match may partly drive team selection that can be exploited by other attacking tactical means.
So corner kicks and the threat posed by them, may have an additional value that stretches beyond the limited goalmouth action they create.
The Value of a corner
Corners are dismissed largely because of their lowly 3-4% conversion rate, but there is no comparable yardstick to other forms of scoring. If we consider corners and their immediate subsequent passes as just another passing sequence, they represent barely 5% of such on-field actions, yet account for typically 15% of the goals scored in a season.
Goal production from final third entries may be a more realistic comparison to corners. Using data from the EPL, a ballpark figure of 50 final third entries are required to score a goal other than one scored from a corner. So if we bundle other methods of scoring into readily recognisable packages to better draw a comparison with corner situations, we see that the efficiency at which they are turned into goals is also extremely low.
To dismiss corners solely on the grounds that they almost always fail to produce a goal neglects to acknowledge that virtually every other on-field action in football almost always fails to produce a goal also.
A penalty kick is the most efficient precursor to a goal, they are converted at nearly 80%, but the event is relatively rare. Corners are much less efficient, but much more common events, while goals scored from final third entries are arguably less efficient than corner situations, but commoner still.
Again using EPL data, on target goal attempts from corner kicks are converted at higher rates than on target efforts from open play. Many of the former are headers, which carry a lower goal expectation than shots from the same position, but attempts from corners are also invariably from closer range. Shot type and distance from goal are the two most influential factors that combine to turn an attempt into a goal.
Rarity and efficiency are the two factors by which a scoring method should be judged and corners more than hold their own with open play alternatives. A successful corner requires two players to connect in an often well practiced routine, so although luck still plays a massive role in scoring from such a set piece, there is scope to also edge the percentages more in your favour with a skilled delivery and a finely rehearsed attacking scheme.
Corners in domestic football allow more talented sides to enhance their already impressive scoring record from open play as the quality of their delivery may be better than average and they also afford the less skilled side a relatively common and achievable route to chance creation.
The worth of goals scored from corners to Greece at Euro 2004 to more recent domestic and European cup winners in Wigan and Arsenal and Chelsea and Real Madrid, respectively, should be noted, along with the detrimental effect such scores had on the chances of their respective opponents.
Corners and goals scored or conceded from them will continue to be influential in deciding the ultimate outcome of tournaments played over a relatively small number of matches, where some sides are guaranteed to temporarily greatly exceed the baseline conversion rate usually seen for corner kicks.