What are “expected goals” (xG)?

To work out a team's “expected goals” (xG) for a match, every shot must be analysed and given an "Expected goal value" (EGV).

EGV is the probability that any given shot will end up as a goal.

As Patrick Lucey, director of data science at STATS, explains, EGV is based on a number of factors, such as where the shot was taken from, the proximity of defenders, the nature of the attack (i.e a direct free-kick or a penalty). The EGV of a shot assumes it is being taken by someone of average ability in the league, so it expects for instance that a shot from 10 yards out plum in front of goal with no defenders nearby has a high chance of ending up as a goal.

From an analysis of every shot's EGV in a match, an "expected goals" (xG) figure can be placed on each team from that match. If a team has a higher xG figure than actual goals scored, it will broadly be because of wasteful finishing or good goalkeeping, or both. Likewise if a team is scoring more than its xG then it could be down to moments of individual brilliance from an attacker or say a goalkeeping error.