The underlap is the better run and the overlap survives because it is easier to teach

Full backs keep sprinting round the outside because coaching an outside run takes ten minutes and an inside one takes a season.

An overlap is a beautiful thing to watch and a fairly modest thing to defend. The full back goes round the outside, the winger holds, the ball is rolled into the channel, and a cross comes in from a position where the defending side already has bodies back and the goalkeeper has a clear view of the flight.

The underlap is harder and worth more. It is also much rarer, and I do not think that is a coincidence.

Run outside your winger and you are attacking space the defence is happy for you to have. The touchline does half the marking. Run inside him, into the gap between the opposition full back and centre back, and you are attacking the space they least want occupied, arriving on a diagonal, facing goal, with a chance of a cutback rather than a hopeful cross. Every defensive coach in the game would rather concede the first run than the second.

So why is the outside run still the default? Because it can be coached as a pattern. The instruction is a sentence. Winger receives, you go round him. It works without much reading of the game and it looks like commitment, which keeps everyone happy. The inside run cannot be reduced that way. It depends on where the far centre back's eyes are, whether the holding midfielder has been dragged across, and whether your own winger is capable of holding a defender still with body shape rather than just taking him on. That is a judgment, and judgment takes years.

There is a workload angle too, and it cuts against the fashionable view. Repeated overlapping runs are among the most expensive actions a full back performs, long high-speed efforts, often unrewarded, and then an immediate recovery sprint in the other direction if the move breaks down. Underlaps are shorter and start from a more central position, which means the recovery distance is smaller. A side that swapped a third of its outside runs for inside ones would probably reduce its full backs' high-speed load and improve its chance creation at the same time.

The reason it does not happen is not tactical conviction. It is that patterns are teachable and reading is not, and coaches are judged on Saturday.