Tottenham and the mystery of the xG: how Bayern Munich defeat defied statistics Despite Spurs suffering a historic 7-2 defeat, the numbers tell a different story of that Champions League night in north London

It was Bayern’s seventh goal against Tottenham that caused the unease. Five goals is a raised eyebrow, six is somehow both scarce and yet common enough that Manchester City have done it 11 times in the Premier League since Alex Ferguson left Manchester United. Seven though… seven is the first number in both English and German to have more than one syllable, it feels big, and in football terms it is big.

And yet soon after Tottenham’s humiliating defeat in the Champions League had concluded it emerged that on Expected Goals, Tottenham, thanks in part to Harry Kane’s penalty, had outscored the visitors, who ended the match with a modest xG figure of 1.45 but an actual goal total of 7 (seven).

First let’s just revisit what Expected Goals is, because although it has been used by football clubs for most of the 2010s and in the media for the last couple of years, it is not yet universally understood. xG is simply a way of counting shots that rates their quality, based on historical analysis of other teams and players to have efforts from the same location and in the same match scenario.

So, a penalty is rated as 0.79 xG because historically around 79 per cent of penalties result in goals. An open goal a couple of yards out will have a very high xG figure, while a long-range effort, say Vincent Kompany’s crucial goal against Leicester last season, will have a very low figure (in the case of the Kompany strike, 0.025, or 2.5 per cent).

At this point some people will raise their hand and point out that certain players, Lionel Messi for instance, are clearly better at shooting from long range than Kompany, so how can the model make sense. But remember, the xG figure is a historical average, and every individual is being compared to that, be they higher, lower or bang average.

No-one, including Sergio Aguero at the time, expected Kompany’s shot to go in but it did. Aguero would have more confidence in his international team-mate Messi, and the numbers back this up: in 2018-19 the Barcelona man scored nine goals from outside the box from a combined xG of 3.46. Shooting from long range is rarely the right choice, but if you’re Lionel Messi then, well, it sort of is.

Back to the Tottenham-Bayern game and we can now appreciate that Bayern’s xG of 1.34 on the day is extremely unusual for a team that scored seven goals, but a combination of luck, judgement, Robert Lewandowski and a Serge Gnabry masterclass saw the Bundesliga side home. Bayern scored with all five of their shots on target in the second half in London, with Hugo Lloris’ last save coming in the 21st minute.

That gap of 5.66 between Bayern’s xG and their goals total is the biggest seen in any Champions League game in the last seven seasons, with the matches than come close usually featuring group stage minnows such as Legia Warsaw, Ludogorets and Celtic.

Interestingly, the nearest comparison involving two heavyweights is also a Bayern game, namely their 7-1 away win at Roma in October 2014. The Italian side was second in Serie A at the time but were swept away by Pep Guardiola’s team who scored with seven of their 11 shots on target. At Spurs last week it was seven of 10. As Guardiola said after the game in Rome: “This is a fluke, it’s not normal to win 7-1.”

In recent Premier League terms, the most similar scenario is Southampton’s 8-0 win against Sunderland in October (yes, it always seems to be October) 2014. Saints’ goal total was boosted by a highly rare three own goals from the visitors, and they ended the match with an xG of 2.98, giving them a difference of +5.02. Anyone who can remember the game, and Santiago Vergini certainly can, will know that it was not an 8-0 sort of match but sometimes football games can get way out of control.

Ultimately the history books will note little more than the score, and in 50 years, anyone looking back at Tottenham’s defeat to Bayern will see that they let in seven goals, not that they were the better team for the first 40 minutes of the game. But for anyone seeking some nuance or solace, xG can shine a brighter light on even the gloomiest of scorelines.

The OptaJoe column is written by Duncan Alexander