Expected Goals assigns every shot a probability of becoming a goal, based on distance, angle, type of chance and defensive pressure. A penalty is worth about 0.76 xG, a long shot about 0.03.

A team can win 1-0 while losing the xG battle 2.4 to 0.5, which tells you the result flattered it. Over time, xG predicts future performance better than raw points or goals alone.