Is Portsmouth’s Expected Goals stat completely pointless?

By Freddie Webb

After being published in the Portsmouth News, Ben Mayhew’s expected goals league table has been ridiculed by Pompey fans.

The table and the expected goals stat (xG) has been branded as pointless: not reflecting their league position and performances.

Mayhew’s current expected goals table has Portsmouth 2nd in League One, by calculating the quality of chances the Blues are expected to score and concede.

Compared to the Pompey’s actual results, defensive lapses and creativity issues, second place is a world away from reality.

In this case, Pompey’s xG and expected goals against (xGA) are misrepresenting how strong Portsmouth are.

But, xG can be used to highlight the patterns of play that many fans have seen in the stands.

Using Wyscout to show the xG stats from League One and video clips from the EFL, I’ll be explaining what xG is, and how it can be used to explain individual and team performances.

The stat has not solved football, but it is far from pointless.

What is xG

Expected goals works out how clinical a shooting chance was by comparing it to a database of previous chances.

The larger the xG, the higher chance a shot becomes a goal.

For example, if a shot has an xG of 0.7, then the same shot would lead to seven goals in ten attempts.

A shots xG is determined by its position and angle.

Examples from the Bristol Rovers vs Portsmouth show how variable xG can be.

John Marquis’ header has a high xG. He is in front of the defender and shooting in the six-yard box.

In comparison, Tom Naylor’s shot has a lower xG.

Naylor’s shot is from outside the penalty area and has two Bristol Rovers defenders in front of him to block the shot.

How should xG be used?

xG is not used for is predicting match results. Instead, xG can give a general indication of which team created more chances and if those chances were clear-cut or not. The stat simply clarifies the pattern of play with a number.

From watching the Bristol Rovers vs Portsmouth, you could tell that until the 75th minute, Pompey had more chances and controlled possession.

Stats should always be analysed in context.

Alongside other stats and video clips, xG and xGA can highlight if a team is creating or limiting enough high-quality chances.

Statistically, Pompey are not far from the play-offs: But problems which are shown on the pitch are also shown in the xG and xGA stats.

Portsmouth’s xG and xGA – What does it say about the team?

It is clear to see Pompey have struggled offensively this season.

The Blues have a strong first 30 minutes but then fail to create clear-cut chances, despite having the lion share of possession in most games.

Players are not supported later in games. Kenny Jackett makes few substitutions and employs a deep defensive line to cling onto one or two goal lead.

When the team drops deep, no options are left to counter-attack with. Kenny Jackett’s entire game plan is to hold onto leads, which only invites trouble.

This strategy used to work when had the best back-four in the division last season, but not anymore.

Although, these issues are not all tactical. Pompey’s attacking players have been inconsistent and have lacked confidence: Not making the most of their chances.

Therefore, Pompey’s xG is average for League One.

The team is scoring less than expected, but they are still not creating enough chances compared to the talent that they possess.

Even the current xG rating is subject to some scrutiny, when in 3/13 of those games, Pompey played against 10 men or less.

The Blues xGA figure is a more positive but frustrating figure.

Pompey have only conceded slightly more than expected, holding the 2nd best xGA in the league with 10.89.

Generally, Kenny Jackett’s defensive set up has been solid ever since he settled on a back four of Lee Brown, Christian Burgess, Sean Raggett and James Bolton.

Although, individual errors have been commonplace this season, especially in the last 15 minutes of games.

Pompey have conceded six goals in the final ten minutes of games. This trend is definitely more than an anomaly.

The defensive set up in the final 10/15 minutes of games has to be changed for Pompey to win games.

Portsmouth’s trends shown in xG and xGA numbers are not lost on the fans, they have seen them already (colloquially known as the eye test).

Offensively, Pompey have been underwhelming and one-dimensional, but defensively solid barring individual errors.

Pushing the defensive and midfield lines further forward is the best change the team can make.

This will maintain Pompey’s defensive solidarity whilst giving the attacking players more support in possession and when counter-attacking.

The team has issues, but the stats suggest that they are not that far away from a play-off spot in the long term.

Whether this will satisfy the Fratton Faithful remains to be seen.

Video clips: Wyscout/EFL

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