xG Explained

What is xG?

Very simply, xG (or expected goals) is the probability that a shot will result in a goal based on the characteristics of that shot and the events leading up to it. Some of these characteristics/variables include:

Every shot is compared to thousands of shots with similar characteristics to determine the probability that this shot will result in a goal. That probability is the expected goal total. An xG of 0 is a certain miss, while an xG of 1 is a certain goal. An xG of .5 would indicate that if identical shots were attempted 10 times, 5 would be expected to result in a goal.

There are a number of xG models that use similar techniques and variables, which attempt to reach the same conclusion. The model that FBref uses is provided by Opta. Opta's xG model includes a number of factors above just factors such as the location and angle. Their model also accounts for the clarity of the shooter's path to the goal, the amount of pressure the shooter is under from defensive players, the position of the goalkeeper, and more. That means that their xG model factors in the defense and goalkeeping when determining the odds of the shot reaching the goal.

Take this Diego Jota goal vs Southampton for example. The shot was taken directly in front of the goal from very close range. It's a very good chance. Using an older model that accounts for location, angle, pass type, and such, it would have a 0.68 xG. However, Opta's model also accounts for the fact that the goalkeeper is out of position and there's no defender in the way, which boosts the xG of this shot even higher, to 0.90.

xG does not take into account the quality of player(s) involved in a particular play. It is an estimate of how the average player or team would perform in a similar situation.

How xG is used

xG has many uses. Some examples are:

Penalty Kicks

Each penalty kick is worth .79 xG since all penalty kicks share the same characteristics. Comparing a player's goals from penalty kicks to their penalty kick xG can indicate a player's penalty kicking ability. Likewise, we can do the same for goalkeepers in these situations.

FBref's xG totals include penalty kicks unless otherwise noted. For xG excluding PK, we recommend using npxG (non-penalty expected goals).

How we calculate xG totals for a single offensive possession

In some cases, a player or team's xG totals do not equal the sum of their shots. For instance, a team may attempt multiple shots in a single possession, but it is likely that these shots are contingent upon the outcome of the previous shot(s).

Take for example, this match between Schalke 04 and Nürnberg:

In the 78th minute, Nürnberg attempted three shots which ultimately led to a goal. Hanno Behrens attempts a shot that is saved, but he is able to take a second shot as the ball is deflected off the defender. The second shot goes off the woodwork, which allows Adam Zreľák to easily tap it in. According to Opta's expected goals model:

The sum of these three shots is 1.67 expected goals, even though it is impossible to score more than one goal in a single move. To solve this problem, we find the probability that the defending team does not allow a goal in this possession. In this case, the calculation is:

(1 - .41) x (1 - .47) x (1 - .79) = .0657 or a 6.57% probability that Schalke does not allow a goal.

To find Nürnberg's xG, we simply subtract that probability from 1:

1 - .0657 = .9343 xG

In other words, we estimate that an average team in a similar situation would be expected to score a goal 93.43% of the time.

We use a similar method when calculating xG for individual players. Adam Zreľák receives .79 xG from his single shot while Hanno Behrens receives:

1 - (1 - .41) x (1 - .47) = .6873 xG

This shows why a team or player's total xG may not equal the sum of the xG from their shots and why a team's total xG may not equal the sum of the xG from their players.

Possessions that include a penalty kick

Similarly, we include shots taken from a rebound after a penalty kick with xG from penalty kicks. Take this Marco Reus penalty kick for example:

Since the second shot is a result of the first, we use the same probabilistic method in the previous example. Rather than a total 1.71 xG (.79 + .92), the calculation is:

1 - (1 - .79) * (1 - .92) = .9832 expected goals

However, since the second shot is also considered to be a part of the penalty kick xG, Reus gets 0 npxG (non-penalty expected goals) on this play.

Note: We treat corner kicks and free kicks as a new possession, not a continuation of the previous possession, but are continuing to study the issue.

What is Post-Shot xG (PSxG)?

Regular xG, or what can be considered "Pre-Shot xG", is calculated considering all shots at the time of the shot without knowing the quality of the shot attempt. It not only includes shots that are on target, but also shots that are deflected or off target. Post-Shot xG is calculated after the shot has been taken, once it is known that the shot is on-target, taking into account the quality of the shot. As with xG, PSxG is provided by Opta and is further explained here.

All shots which are off target will have a PSxG of zero since there is a 0% chance that this trajectory will lead to a goal.

When evaluating a goalkeeper's shot stopping ability, we only want to include shots that are on target since these are the shots where the goalkeeper can have an impact. Therefore, we use PSxG to estimate the quality of shots in which they have faced.

What is xA (expected assists) and xAG (expected assisted goals)? How do they differ?

xA, or expected assists, is the likelihood that a given completed pass will become a goal assist. This statistic developed by Opta assigns a likelihood to all passes based on the type of the pass, the location on the pitch, the phase of play, and the distance covered. Players receive xA for every completed pass regardless of whether a shot occurred or not.

In order to just isolate the xG on passes that assist a shot, there's Expected Assisted Goals (xAG). This indicates a player's ability to set up scoring chances without having to rely on the actual result of the shot or the shooter's luck/ability. Players receive xAG only when a shot is taken after a completed pass.

We use xG+xAG for goal contributions since players' goal contributions are typically Goals + Assists and this better matches that standard.

Previous to October 2022, we used xA to mean expected assisted goals (now xAG). When we switched our data provider to Opta, they provided their version of xA described above. We made the name change to xAG. Opta: What are Expected Assists.

Where to find xG

Team xG, xG against, and xG difference can be found on league tables, such as this:

Premier League Table
Rk Squad MP W D L GF GA GD Pts xG xGA xGD
1Manchester City3832249523+729884.324.7+59.6
6Manchester Utd38199106554+116661.450.6+10.8
9Leicester City38157165148+35252.443.7+8.7
10West Ham38157165255-35247.661.9-14.3
12Crystal Palace38147175153-24947.650.1-2.5
13Newcastle Utd38129174248-64539.153.6-14.5
18Cardiff City38104243469-353442.461.5-19.1

Player xG, npxG & xA can be found on team pages, such as this:

Standard Stats 2018-2019 Manchester City: Premier League Table
Playing Time Performance Expected Progression Per 90 Minutes
Player Nation Pos Age MP Starts Min 90s Gls Ast G+A G-PK PK PKatt CrdY CrdR xG npxG xAG npxG+xAG PrgC PrgP PrgR Gls Ast G+A G-PK G+A-PK xG xAG xG+xAG npxG npxG+xAG
Edersonbr BRAGK2438383,42038.0011000200.
Aymeric Laportees ESPDF2435343,05734.0336300303.
Bernardo Silvapt PORMF,FW2336312,85431.77714700307.47.47.815.21521562770.220.220.440.220.440.230.250.480.230.48
Raheem Sterlingeng ENGFW2334312,77130.81792617003013.713.79.623.3155874360.550.290.840.550.840.440.310.760.440.76
Sergio Agüeroar ARGFW3033312,45927.32182919224018.
Kyle Walkereng ENGDF2833302,77930.9112100300.
David Silvaes ESPMF3233282,40126.76814600207.87.88.516.31182702220.220.300.520.220.520.290.320.610.290.61
Fernandinhobr BRAMF3329272,37726.4134100501.
İlkay Gündoğande GERMF2731232,13723.7639600304.
Leroy Sanéde GERFW2231211,86720.71010201000106.76.77.414.184673410.480.480.960.480.960.320.360.680.320.68
John Stoneseng ENGDF2424201,76419.6000000100.
Riyad Mahrezdz ALGFW,MF2727141,34314.97411701005.
Nicolás Otamendiar ARGDF3018141,23613.7000000101.
Oleksandr Zinchenkoua UKRDF2114141,15112.8033000100.
Vincent Kompanybe BELDF3217131,22413.6101100600.
Kevin De Bruynebe BELMF27191197510.8224200201.
Benjamin Mendyfr FRADF24101090010.0055000100.
Danilobr BRADF271198079.0101100100.
Gabriel Jesusbr BRAFW212981,03611.573106111011.210.52.312.735211280.610.260.870.520.780.970.201.170.911.11
Fabian Delpheng ENGDF281187258.1011000110.
Phil Fodeneng ENGMF181333353.7101100002.
Philippe Sandlernl NEDDF2100
Arijanet Muricxk KVXGK1900
Claudio Bravocl CHIGK3500
Squad Total26.7384183,42038.09171162883444184.381.365.5146.71325242924122.391.874.262.324.182.221.723.942.143.86
Squad Total26.7384183,42038.09171162883444184.381.365.5146.71325242924122.391.874.262.324.182.221.723.942.143.86

Expected goals can also be found on a number of different pages such as league player stats, match reports, player pages and player match logs.

FBref Competitions with xG Data