Tuesday 9 July 2013

Headers As A Valued Scoring Method.

About this time last year I wrote a piece in defence of the art of crossing the ball at a time when crossing was usually randomly juxtaposed with "aimless" and was considered the first and often also the last resort of the technically limited, be it Stoke in the Premiership or England on the international stage.

Appealing though the sentiment may be, aesthetics win no extra points. Crosses, despite their inefficiencies and possible reliance on more luck than perceived inevitability, remain an essential component of a balanced attack and unashamedly, a route to mid table respectability for those sides that are less able to attract sufficient numbers of technically skilled players to try to play Barcelona lite. There is also enough of a spread in crossing completion rates to entertain crossing as a repeatable talent.

Inevitably, headers, the most visible product of a cross have shared the opprobrium heaped on their precursor. So let's try to rehabilitate headers.

The first knock that headers have to try to repel is that they are less likely to result in a goal than a similarly positioned shot and this is easy to confirm. Self collected shot expectancy models are currently limited in their usefulness by an almost absence of defensive data, but they are sufficient to speculate as to the likely pecking order for goal attempt types. Head the ball from almost any position in and around the box and a similarly positioned attempt with the feet in open play will, on average prove to be a more rewarding proposition.

If we use shots generated from open play as the standard bearer for goal attempts and compare the goal expectancy for other types of attempts to this most usual product of a ground based attack, we can illustrate the relative potency of different scoring attempts. Headed goal attempts from either set pieces or open play spread inside and outside of the area, on average see their likelihood of scoring decreased to around a third of that for a shot from the exact same pitch position. But is this sufficient evidence within a proper context to dismiss headers completely ?

The standout goal attempt in the above plot is for a direct shot from a free kick, it is around twice as likely to see a goal scored compared to the cultural elite's weapon of choice, a shot from open play. ( A penalty kick, if included would be off the scale shown here). So under this initial cross examination, open play shots beat headers, but direct free kicks then beat open play goals, (and penalty kicks would trump everything).

But only in this context-less vacuum of a goal expectation model.

Arrow length denotes goal expectancy for each average attempt type.
Direct free kicks fail to confirm their early promise in the race to be the most productive method of scoring. Firstly, although a direct free kick from a central position on the edge of the box is almost twice as likely to result in a score than an identical shot from open play, that is the limits of a direct free kick's scoring ambitions. Because of their nature a direct free kick cannot venture into the penalty area.

A free kick struck, first time, from the average position for all direct attempts in my sample has about a one chance in twenty of producing a goal, much better than an identical effort from open play, where success rates fall to nearly one in 50. So despite the impressive initial plot, once we add context that includes real life experience, we realize that we are merely doubling our chances on a long shot. Reality bites even deeper if we then include the relative rarity of direct free kicks, they account for around 5% of a side's total goal attempts. Try as some teams might, it doesn't appear possible to build a strategy around creating large numbers of direct free kicks, outside of the box.

Frequency of attempt and average position from where those attempts originate in reality, along with the ability of teams to alter those parameters are the bare essentials to consider before we should be passing judgement on a method of attempted scoring. Shots generated from open play use their ability to be performed inside the penalty area to get closer to the goal, but not by very much. While headers, be they created in open play or from more attack friendly set plays, on average, threaten the no man's land for keepers between the penalty spot and the six yard line, open play shots barely creep past the edge of the box itself.

In short, headers appear to get you closer to the intended target, but defenders or anxious strikers are kept at arms length when teeing up a shot. The advantage of creating chances closest to the goal appears to lie with headed opportunities. Of the four different attempt categories, by virtue of the distance and width from the goal from where they originate, the average header, following a set play, has the best chance of providing a goal. Relatively distant and defensively harried, open play shots, based on average shot position are now the lest likely to provide a goal from their average point of execution.

Only frequency of attempts can now restore open play shots and elevate them back above headed attempts.

And it does. Open play shots account for around 60% of goal attempts, headers, from set or open play, just 20%. If we add frequency of attempt to average position, open play shots account for around half a goal a typical game, around twice the tally for the category of headers described here. So shots in this ballpark assessment, on average is a superior scoring method compared to headers, but the contribution for the latter remains significant and greatly outstrips that made by other goal attempts, such as direct free kicks.

Chill Guys. It's "only" going to be a header.
Headers, as has been mooted contribute to a diverse attacking strategy, their goal contribution is not insignificant and ignorance (through lack of detailed data) of the outcome of breakdowns in attempts to generate open play shooting opportunities may obscure an advantageous residual value for a failed cross. Failed crosses are there for all to see, but may result in possession being maintained or quickly regained, while failed attempts to create open play shots may go disguised and unrecorded as simple losses of the ball. We simply don't have enough detailed data to know with any authority.

Judging the effectiveness of headed goal attempts merely on the indisputable evidence that shooting is almost universally preferable to a header from the same spot on the pitch is to ignore the realities of the game. Headers are a starting point for the less technically adept to hone in the hope that continued, but limited success may attract better quality players, but it may also provide the wrinkle that prevents pass orientated sides from drifting into tactical stagnation.

1 comment:

  1. So if a team were to use half the direct free kicks aimed at goal, as crosses into a packed box, the chance of scoring would go up. More so if the cross was curled towards the target. But would that then count as a cross or a shot?