xG, or expected goals, is an assessment of the quality of created scoring chances. Each shot is assigned a probability of becoming a goal based on position, distance to goal and other factors. The sum of these probabilities forms the team’s xG value.
How to understand xG
If the teams’ xG is 2.4 and 0.6, it means the first team created significantly more dangerous chances. At the same time the actual score can be anything — for example 0:1. xG evaluates the quality of chances but does not determine the match result.
How to use xG in analysis
- Compare the teams’ xG to understand which of them created more dangerous chances.
- Compare xG with actual goals to assess the conversion of chances.
- Study the metric over a series of matches: the data of a single game can strongly depend on random events.
Limitations of the metric
xG primarily takes shots into account, but does not always fully reflect the course of the game. Red cards, early goals, tactical changes, team line-ups and other factors also affect the result. Moreover, different data providers use different models, so their xG values may differ.