Average defensive line height is a number that describes no actual moment

A back four that sits deep and then jumps thirty metres has a mean line position it barely ever occupies.

Forty-two metres from goal, on average. The line was almost never there.

A defensive line does not hover at a stable height. It sits, it steps, it drops, and in a well drilled side it does these things suddenly and by agreement. Plot line position over ninety minutes and you often get two clusters rather than one: a deep resting position for settled opposition possession, and a much higher position taken when the pressing shape is triggered. The mean sits in the valley between them, describing a configuration the defence deliberately spends as little time in as possible, because the space between the two positions is the vulnerable one.

Averaging a bimodal distribution is one of the reliable ways to produce a number that is arithmetically correct and descriptively false. It happens throughout football analytics and this is the cleanest example of it.

The consequence is real. Two teams can report the same average line height while playing completely different games. One holds a medium block consistently. The other alternates between very deep and very high. Any comparison based on the mean says they are alike. Anyone who has watched them knows they are opposites, and the analysis has quietly contradicted the eye test while being wrong.

Standard deviation would help a little, and hardly anyone reports it. What would help more is the shape: publish the distribution, or at least the proportion of defensive phase time spent above and below a couple of reference heights. That takes three numbers instead of one and it separates the two teams immediately.

The same criticism applies to line compactness, block width and almost every spatial summary in the tactical vocabulary. They are all reported as means because a mean fits in a table cell. Most of them are describing behaviour that switches between states rather than varying smoothly around a centre.

I would push it further. Where a team's shape genuinely does have modes, the interesting statistic is not the position of either mode but the transition: how quickly the line moves between them, and how often the movement is ragged rather than collective.

That is where goals come from. Not from the line being high or low, but from it being caught halfway, which is exactly the value the average reports back to us as though it were the team's habit.