Compactness is measured across the pitch when it should be measured up it

Defensive blocks are judged on how narrow they are, and the distance between the lines is the number that decides matches.

Say the word compact and most people picture a defence squeezing towards the middle. Narrow. Shoulder to shoulder. Bodies in the middle of the pitch and the opponent forced to go round.

That is one axis, and it is the less important one.

The vertical dimension is what actually decides whether a block holds. The distance between the deepest defender and the highest midfielder determines whether there is any usable space between the lines, and it is the space between the lines that good attacking sides are hunting for. A block that is beautifully narrow but thirty metres deep from back to front has a corridor running across it that a decent number ten will find within about four minutes. A block that is slightly too wide but tight vertically forces the ball backwards even though it looks untidy on the broadcast angle.

The reason horizontal compactness gets the attention is that it is visible. You can see narrowness from a standard camera position. Vertical compression happens along the axis the camera is pointing down, so it foreshortens and mostly disappears, which is why analysts who work from a tactical camera above the halfway line reach very different conclusions from the ones working from broadcast footage.

Holding the vertical distance is also the harder job, because it requires the back line to push up at the exact moment the ball goes backwards, and pushing up is frightening. One defender who hesitates stretches the whole block, and the hesitation is usually rational, because he is the one who gets blamed for the ball over the top. So the line drifts back a metre a minute, nobody makes a decision, and by the seventieth minute a side that started with a twenty-metre block is defending a thirty-five metre one and wondering why the opposition midfielder suddenly has time.

If I were auditing a defence I would ignore shape screenshots entirely and plot one thing over ninety minutes. The gap between the last defender and the deepest midfielder, sampled every second. Sides that concede late almost always show the same curve, and it starts long before the goal.

Narrow is easy to coach because it is easy to see. Short is the one that wins.