A key principle in my approach to football analytics is to make sure that all data is related back to the game itself. We should never introduce a number, a statistic or a metric unless we can say what it means in terms of a player’s actions and coaching decisions. We have already seen this principle at play in Guardiola’s organization of resting defence, the way we evaluated Traore in terms of high-speed dribbles and space creation by Manchester United’s left-back, Luke Shaw.
We now look for the same principles in the way we use expected goals. Without these principles the numbers don’t tell us anything.