What is xG in football and how does it work?

Expected goals (xG) is a metric used to determine how likely a player is to score a chance and to calculate how many goals a team is expected to score in a match.

The metric was invented in 2012 by Opta's Sam Green and has become commonplace across football analytics.

In xG, every shot a player has is given a score between zero and one. The higher that number is, the more likely a team is to have scored that particular chance.

This information is calculated from Opta's historical data from nearly one million shots.

The data model then generates a calculation on the percentage chance the player is likely to have scored in the same scenario.

Other factors taken into consideration include distance, angles, goalkeeper position, the positions of other players, shot type, pattern of play and the previous action.

For instance, a chance that has an xG of 0.2 means that a player had a 20% chance of scoring from that opportunity. A chance with an xG of 0.8 would represent an 80% chance of scoring.

Those xG figures are then added up to determine how a player or team has been performing collectively during a match or season.

The data metric has been criticised by some supporters, pundits and managers, but it is seen as a good indicator of how a player or team has been performing in front of goal.

Yes, xG is often used by data teams at football clubs to help determine whether or not they have been taking their chances or not. The model can add further context towards a result rather than just the score itself.

It also aids clubs in their recruitment. For the 2024-25 season, forwards Bryan Mbeumo and Matheus Cunha were two of the top overperforming for goals compared to their xG models for the season in the Premier League. Manchester United signed both shortly after the season ended.

Ahead of signing Mohamed Salah in 2017, then Liverpool manager Jurgen Klopp was more interested in signing Julian Brandt from Borussia Dortmund.

After being convinced by Liverpool's analyst, whose reasons for preferring Salah included his xG values, Salah was signed and has gone on to win four Premier League golden boots in eight full seasons with the club.

Gary O'Neil often referred to expected goals metrics during his time as Wolves' head coach, while ex-Everton boss Sean Dyche also spoke about it last season when giving context to a defeat to West Ham.

Thomas Frank, Daniel Farke, Eddie Howe, Thomas Tuchel and Pep Guardiola have all also discussed xG and its uses in recent years.

Expected goals statistics have led to the berth of other similar metrics to record different sets of data.

Expected goal difference (xG minus xG allowed) helps indicate how a team should be performing in matches and across a season.

xG can also be narrowed down to open play and set-pieces, while non-penalty xG is used to determine a team's expected goals without penalties.

For goalkeepers, xG prevented can be used to determine whether they are conceding more or fewer goals than they should be.

Expected assists and post-shot xG are also among the growing number of xG-related statistics.

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