Judge a defensive block by how fast it slides, not how narrow it sits

Compactness photographs well in a still frame and tells you almost nothing about whether the shape can survive a switch of play.

Freeze any match in the eighty-second minute and you can measure a block: distance between the highest and deepest outfield player, width of the middle four, gaps between the lines. Coaches love these numbers because they are easy to check and easy to correct. Get tighter. Get closer to your partner. Come across.

The problem is that a narrow block is a bet. You have decided to concede the far side and to buy it back with speed when the ball goes there. If the buying back is slow, you have not built a compact defence, you have built a compact target with thirty metres of grass next to it.

So the number I would want is transit time. Ball leaves the right centre back, travels to the left winger, and the question is how long the far side of your block takes to be square again. Two seconds is a defended flank. Three and a half is a cross from a standing start with your full back arriving as the ball does, which is the same as no defence at all with extra running.

Sliding time is a different quality from compactness and it is trained differently. It rewards a midfield that starts moving on the passer's body shape rather than on the pass, and it punishes any player who ball-watches for half a beat. It also depends on something unfashionable: who is furthest from the ball and whether he is jogging or walking. Almost every slow slide I have watched back begins with one player at the back of the shape treating the switch as somebody else's problem for a second and a half.

There is a legitimate other view. Some teams deliberately accept slow slides because they would rather force play wide and defend crosses than be split centrally, and against a side without a genuine crosser that is fine arithmetic. I would just want it stated as a choice rather than discovered as a weakness in April.

The bit that irritates me is the graphic. Broadcasters show a shaded polygon of the defensive shape, frozen, with an area figure attached. It is a photograph of a moving thing. Show me the same shape a second after a switch and you would have a genuine argument on screen.