The intuition
xG assigns each shot a probability of becoming a goal based on historical outcomes of similar chances — angle, distance, body part, defensive pressure and assist type.
Why single-match xG is misleading
Over 90 minutes, variance dominates. A team can generate 2.4 xG and score zero. Over 10 matches, the noise collapses and xG differential correlates 0.78 with points-per-game.
Using xG responsibly
xG is a description of chance quality, not a forecast of a single match. Treat it as one input inside a broader analytical framework.