xGoals and penalties: are penalty takers getting better?

In Simon Rolfes, the Bundesliga and its partner AWS have an expert who knows the Bundesliga from A to Z. Bayer 04 Leverkusen's Sporting Director, Rolfes wore Die Werkself's colours 288 times between 2005 and 2015, and represented Germany on 26 occasions. Rolfes is the ideal man to write a weekly column for the 'Bundesliga Match Facts Zone' on bundesliga.com, analysing current trends and giving unique insight on the Bundesliga Match Facts.

Here, he looks at xGoals and the peculiar case of penalties.

By Simon Rolfes

What do Bas Dost, Wout Weghorst, Silas Wamangituka, Marcel Sabitzer, Vincenzo Grifo and Lucas Alario all have in common? All six of them took – and converted – penalties on Matchday 11. But why did that catch my eye in particular?

In order to explain xGoals, the example of penalties is often used. That has a very simple reason: while it is difficult to reproduce a goalscoring situation in open play, the conditions for a penalty are always the same – the spot is 11 metres from goal, the posts are at an angle of 37 degrees from the penalty taker, who has only the goalkeeper to beat.

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Analysis of thousands and thousands of penalties shows us that the probability of scoring from the spot is around 77 per cent. In terms of xGoals, that equates to 0.77. My own experience confirms this – I took plenty of penalties in my Bayer Leverkusen days, both in games and in training, and I converted an average of about seven or eight from every ten.

The 2020/21 season is telling a different story, however. Up to Weghorst's miss on Matchday 7, all other penalties had been converted, extending a perfect record of 35 straight scored penalties including those from the end of last season. That's the best run in history! This season, 39 penalties have been scored from a total of 44, equating to a success rate of 89 per cent – far in excess of the customary penalty-scoring probability of 77 per cent. So the question is: are the penalty takers becoming more assured?

In my opinion, there are two reasons for this development. On the one hand, it is down to the fact that games are being played behind closed doors. Of course it makes a difference to a penalty taker if the stand behind the goal is empty or if it is filled with 20,000 fans of the opposition, deafening you with their whistles. The fact that there are actually millions more watching from the comfort of their own homes is something that you are able to blend out in such a situation.

Watch: xGoals and the art of Goal Probability

What I believe is an even more decisive factor, though, is that many penalty takers – especially in the past few months and years – have changed their technique. Five years ago, it was normal to see goalkeepers diving for one corner early. That way, they were giving themselves a fighting chance of reaching even the best-placed of penalties, assuming they guessed correctly.

Nowadays, though, many players are delaying their run-up to the ball in the final strides. This gives them an opportunity to see which way the goalkeeper is going to go. If the goalkeeper does commit early to one corner, the taker just has to tuck the ball into the opposite one. Goalkeepers are therefore being forced to stay on their feet for longer, meaning they will never then be able to reach a penalty that is placed accurately in either corner.

Watch: Robert Lewandowski and the perfect penalty

This requires a lot of coordination on the part of the penalty taker. They need to slow their run down, keep an eye on the goalkeeper as well as the ball, and make a late decision which way to shoot. On top of this, they of course need to ensure they place their shot well. Bundesliga players such as Robert Lewandowski, Max Kruse or Matheus Cunha have got this technique down to a tee.

As a result, Lewandowski has an 87 per cent success rate from the penalty spot, Kruse 94 per cent and Cunha even a perfect 100 per cent.

If this trio inspires others to take their penalties the same way, the xGoals value for penalties may well be heading higher in future.