Expected Goals
xG
A model estimate of how often similar shots became goals in historical data.
Definition
A shot worth 0.25 xG comes from a place where similar shots became goals about one time in four. The model usually uses location, angle, body part, and sometimes pressure or assist type. It does not say this exact shot should score.
xG is best for describing chance quality across samples. It is weakest as a single-match verdict. Models differ by vendor. Small samples are noisy. Many public models only partly see build-up quality before the shot.
Caution
Do not treat one xG edge as proof of who deserved the result. Keep shoot-outs separate from open-play totals. Label set pieces and penalties before summarising match xG.