We scout defenders for a top speed they never reach

A centre-back is judged on a sprint number produced over forty metres in a game that rarely gives him fifteen.

A recruitment meeting will produce a maximum velocity figure for every centre-back on the list, and somebody will say this one is quick and this one is not, and a transfer will partly turn on it.

Top speed takes roughly thirty to forty metres to reach from a standing start. How often does a centre-back get thirty uninterrupted metres in a straight line? Once or twice a match, maybe, on the genuine footrace that everybody remembers because it is the one that ends in a goal or a heroic tackle.

The rest of his defending happens in the first ten metres, from a standing start or worse, from a backwards start, and almost always with a change of direction in it. That is acceleration and it is a different quality with a different physical basis. Plenty of players with modest top-end numbers are lethal over five metres, and plenty of very fast ones look slow because they take too long to get going and cannot turn.

Then there is the part that is not physical at all. The recovery run that saves a goal is usually won by the angle, not the speed. A defender who reads the through ball half a second early and sets off on a diagonal that cuts the attacker's path does not need to be faster than him. He needs to be running to where the ball is going while the attacker is still running to where the ball is. That half second is worth more than any sprint figure and it is a product of scanning, positioning and having seen the situation a thousand times.

Which is why the old slow centre-back keeps surviving long after everybody has written him off. He is never in a footrace. He arranges not to be.

The argument against me is real. Against a genuinely elite runner in behind, in a high line, geometry runs out and you just need legs, and a side that plays forty yards up the pitch cannot carry a defender who has none. Fine. That is a systems question, and the answer is to match the profile to the line height rather than to buy speed as a virtue in itself.

We keep testing defenders at a distance the game does not use, then acting surprised when the fast one gets turned inside out by a striker who moves first.