In performing some of my shooting analysis work I have struggled with how best to deal with headers.
It is obvious that, on average, headers are taken from locations closer to goal than non-headed attempts on goal (these non-headed attempts will be defined as “shots” during the rest of this piece). That alone would be enough to ensure that we shouldn’t group together headers and shots when undertaking any aggregate analysis.
The combining together of shots and headers is even more problematic when we consider that they may have different outcome profiles even when taken from similar locations. This realisation has had some recent airings on Twitter, so I thought I would use the data that I have collected from the Big 5 leagues last season to put on record just how a header compares against a shot.
When looking at all shots and all headers we can see that there is only a negligible difference in the amount of each type that are on target (34% of headers vs 33% of shots). However of those on target attempts, a header is more likely to be scored than a shot (12% v 9%). It is no surprise to see that headers are blocked much more infrequently than shots; shots are blocked approximately three times as often as headers.
So, if headers are scored at a higher rate than shots, does that mean that, given the choice we would prefer our team to be having a headed attempt at goal rather than a shot struck with the foot?
I would suggest that the answer to that question would be “no”. The main driver of why headers are converted more frequently than shots is due to the location of where the attempts originate.
Location of Attempts
Almost 95% of all headers are taken from the central portion (within the width of the 6yd box) of the penalty area, this compares with just 25% of shots. Virtually no headers are taken from outside the penalty area; whereas more than 54% of shots originate from these longer distances.
At this stage, it’s now easy to see why headers are converted with greater frequencies than shots.
How would the conversion rates for shots and headers compare if we looked at like for like, ie removed the location basis that is inherent with headers?
Inside 6yd box
Shots taken from inside the 6 yard box are converted at 40%, compared to less than 25% for headers. So within these close range locations headers were scored only 62% as often as shots were.
One other takeaway from this grouping of shots is that less than 40% of headers from this extremely close location were put on target. Presumably this is indicative of the pressure that is applied to headers that are attempted from such close range.
Other Central Locations Inside Penalty Area
This time we are looking at shots within the central portion of the penalty area, but beyond the 6 yard line.
Once again, shots are converted at vastly superior rates to headers. This time the conversion rate for shots is almost double that of headers at 20% and 10% respectively. As before, we can see the difficulty that headers have in even just hitting the target.
Sides of Penalty Area
Now turning our attention to shots / headers that were struck from the sides of the penalty areas (outside the width of the 6 yard box) we can see the familiar pattern continuing as yet again shots are converted at twice the efficiency of headers.
In writing this article I set out to determine how much less likely a header was to score than a shot. Without adjusting for shot location headers are scored at a greater rate to those of shots. However, in respect to this particular topic the devil is in the detail as we determined that when shots and headers that were struck from similar places were compared the conversion rate for headers was only approximately half of that for shots.
This is a fact that should be remembered by anyone interested in the analytical side of football
Perhaps I could go as far to suggest that with shots and headers having such vast differences in conversion rates, perhaps the time has come for shots and headers to be disclosed separately in post match statistics instead of them being aggregated together as is the current norm.