Expected Goals Explained – The Ultimate Guide To xG (2020)

Most people have heard or seen Expected Goals (xG) mentioned on the popular BBC programme Match of the Day (MOTD). Many people are confused by the metric, but its meaning is very simple. Expected Goals is essentially a way to qualify and sum up chances in football. The metric is becoming increasingly popular, making its way to TV analysts’ desks and being used more and more by Premier League clubs.

In this article we explain all you need to know about Expected Goals (xG), including what it is exactly and the different variations, how to calculate it, how we can apply it to sports betting and more.

Advanced Metrics (the term used in relation to the analysis of sports to measure in-game productivity and efficiency) are already utilised within many sports around the world – most notably Baseball, Basketball and American Football. Now, they are making their way into mainstream football in the form of Expected Goals.

 

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What Is Expected Goals xG?

‘Expected Goals’ (symbolised as xG) is a measure – usually expressed as a number between 0 and 1 – on whether a given shot will result in a goal. It takes into account a range of factors and historical data and allows us to identify how many goals a player or team should have scored based on the quality of chances they had during a game.

For a visual explanation of expected goals you can watch this brilliant video by the awesome guys at Tifo Football:

 

 

 

Expected Goals In More Detail

An xG of 1 is the highest value a single shot can be, which implies that a player has a 100% chance of scoring. The higher the value of the xG, the more likely the player is to convert the opportunity.

The use of npxG (Non-Penalty Expected Goals) is particularly useful as it provides a more accurate analysis. Since penalties have an xG of 0.76, they can significantly distort both a player’s and team’s expected goals. Since the penalties may not have been earned or deserved, they can provide an inaccurate look to the data. Reading further detail on Expected Penalty Goals (xPG) will also give you a clearer idea of how you can work out the xPG for each penalty in a game.

Prior to expected goals, statistics such as ‘Total Shots' and specifically ‘Shots On Target' were used when analysing a match, and similarly to a final scoreline, they can be deceptive when considering that a shot with an xG of 0.13 classed as the same as a shot that has an xG of 0.83.

For example, let's imagine that Team A took a total of 17 shots during a game while Team B only took 8. From these stats, we would be under the impression that Team A deserved to win. However, if we looked at the expected goals data, we would see that Team A had an xG of 1.34 from the game while Team B had an xG of 2.18.

One popular criticism of the data is that current models do not take into consideration the talent levels of:

  • The player shooting
  • The player in goal

This is something that will obviously influence the xG value when it is implemented and is therefore something to keep in mind.

How Is Expected Goals Calculated

 

Expected Goals (xG) Explained

 

There are a range of different models used to measure expected goals, ranging from the simple to the complex. For example, Opta, the world’s leading supplier of sports data, analysed over 300,000 shots to help create their model.

Below is a video of Opta's Duncan Alexander discussing the xG metric and how it can help us better understand team and player performance.

 

 

The variables that are taken into account when determining the likelihood of a goal include:

  • Distance from goal – Generally, the closer you are the higher the xG.
  • Angle of the shot – Generally, the more acute the angle, the lower the xG.
  • Shooting part – Was it with the strong foot, weak foot or a header?
  • Passage of play – Was it from open-play or from a set piece?
  • Chance creation – Did the opportunity come from a cross, a through ball etc?
  • The shot – Was it from a rebound, did it come after beating an opponent etc?

While these provide a good standard for expected goals analysis, some of the more complex models also take into consideration factors such as the defensive play of opponents. Defending is just as big of a factor in a game as attacking is, so by taking it into account, the data is likely to be more reliable.

 

 

Team xG versus Player xG

xG is calculated in several variations for both players and teams.

Player xg Stats

xG stats for players usually include Expected Goals (xG), Non-Penalty Expected Goals (npxG), and Expected Goals Assisted (xA).

Expected Goals (xG)

The volume of goals that either a player or team will be expected to score based on the factors that a model takes into consideration.

Non-Penalty Expected Goals (npxG)

The total expected goals minus any expected goals from penalty attempts.

Expected Goals Assisted (xA)

The total number of assists a player should have produced based on expected goals taken directly from their passes.

Team xG Stats

xG stats for teams usually include Expected Goals For (xGf), Expected Goals Against (xGa), and Expected Points (xPts).

Expected Goals For (xGf)

The amount of goals a team is expected to have scored based on the expected goals data.

Expected Goals Against (xGa)

The number of goals a team should have conceded based on the expected goals data.

Expected Points (xPts)

The number of points a team is expected to have won in correlation with the expected goals data.

 

How To Apply Expected Goals To Sports Betting

Expected goals data is advantageous to sports bettors as it provides information that a final score may not always reflect.

Football is generally a low scoring sport and as such, goals come in a small commodity, meaning the final score of a game can be misleading.

For example, you may see a team dominate a game in possession, territory and chances created, yet somehow still manage to lose. The basic goal data (final score) will, therefore, be unrepresentative of the game and thus can't be used to form an opinion on future fixtures.

Nevertheless, what can be used for future purposes is the xG goals data that has come from the game. Using this data we can remove any perils about the likelihood of finishing at both ends of the pitch and get a more reliable interpretation of a team’s overall quality.

Short-Term Profit

With regards to upcoming matches, expected goals data can help us identify value. If a team has been over-performing or under-performing their xG metric, they are likely to soon return to their average.

For example, let's imagine Team A has picked up only 1 point from their last three games despite comfortably beating all three of their opponents on the expected goals data. Due to this poor run, Team A are priced at greater odds to win their next fixture than what the data suggests. This would represent value.

While xG data can and should only be used as a guideline, if it supports your research and you believe a price is deemed value, then it is likely to be a good bet.

Ante-Post Betting

There is always money to be made in ante-post markets and by using a system rather than going on gut instinct, you are more likely to be successful.

While you can use the expected goals data to predict upcoming matches, it can also be used for forecasts, such as table standings and golden boot standings.

By using xG goals data both for and against from previous campaigns, we can create an alternative league table, which provides an informative display of how the season went and can help us predict future performance.

However, when using this data for future predictions, it is important to remember that these statistics do not take into consideration factors such as transfers, injuries, form and new managers.

 

Where to find xG stats

There are plenty of websites where you can find xG stats for almost any league you need – we recommend that you take a look at the most relevant sites we have compiled for UK punters. Fbref.com and Understat.com are two of the most popular.

Expected Goals xG Champions League

FBref has some of the best xG stats for the Champions League.

Expected Goals xG EPL

Understat has great xGstats for the EPL, including individual players.

Expected GoalsxG League One

Check out FBref for the best xG stats for the EFL League One.

Expected GoalsxG Championship

We also recommend FBref for the best xG stats for the EFL Championship.

 

Expected Goals FAQs

🎲 How is xG calculated?

xG uses metrics such as Distance from goal, Angle of the shot, Shooting part, Passage of play, Chance creation to calculate how likely a goal will be scored from any position of situation. Statisticians use an Expected Goals formula to create a score between 0 and 1. For example, a shot with 70% chance of creating a goal gets 0.7.

💲What does expected goals mean on MOTD?

It is a metric that shows how likely a goal is from a shot in any position and situation. 0 means zero percent chance, while 1 means 100% chance. Thus, it is a score between 0 and 1. For example, a shot with 34% chance to get a goals has expected goals of 0.34. These expected goals can be added up to show how many chances, a team or player got, and how valuable they were.

🍒 What is xG and xA?

xG is the expected goals for a shot. In other words, how likely it is for a goal to result from a shot in a particular situation and position. You often see it as the sum of the expected goals for a player or team. xA is the total number of assists a player should have produced based on expected goals taken directly from their passes.

 

ThePuntersPage Final Say

In essence, expected goals is a way of assigning a ‘quality' value to every goal-scoring opportunity, based on the information available. There has been a serious amount of growth in the modelling of xG and as time goes on, the more data that is collected, the more reliable and accurate the metric will become.

It is important to remember, however, that the analysis is not always 100% representative of a situation and there will therefore always be outliers.

Football fans, managers, and punters are still divided on the utility of the metric; however, expected goals is here to stay.