A measure of the chance
Expected goals assigns a probability to a shot based on the information a model uses. A shot valued at 0.20 xG represents an estimated one-in-five scoring chance in comparable circumstances. Adding those values describes the chances created; it does not change the actual score.
Models are not interchangeable
Providers can use different inputs and training data. Shot position, angle, body part and the preceding action may be included; more detailed models may also account for defenders or goalkeeper position. Compare teams using the same provider and definition rather than mixing numbers from different sources.
Separate penalties and game state
Penalties can materially change a short run of xG totals. Non-penalty xG can help isolate other chance creation. A team protecting a lead may concede possession and low-quality attempts, while a team chasing the game may take more risks. Read the total alongside that context.
Avoid turning xG into a promise
A team that creates more xG can still lose. Repeated overperformance or underperformance may reflect finishing, goalkeeping, model limitations or chance. A short sample cannot reliably distinguish those explanations. xG is one input to an assessment, not a ready-made prediction.