Nobody has decided whose job the half-space runner is

The most reliable way to score against an organised defence is to attack the seam where two defenders each expect the other to go.

Ask a fullback who picks up the midfielder running beyond him on the inside. He will say the six. Ask the six, and he will tell you he cannot leave the centre of the pitch, and that the fullback should tuck in.

Neither of them is wrong. That is the point, and it is the single most productive weakness in modern defending.

The seam between a fullback and a centre-back is a handover zone, and handovers are where systems fail. A defensive shape can be perfect and still contain one area where responsibility is shared rather than owned, and shared responsibility under time pressure is another way of saying nobody moves. Attacking coaches worked this out years ago, which is why so much of the choreography in the final third is built around getting a runner into that seam from the blind side.

From the blind side is the operative phrase. A runner who starts in front of the fullback is trackable. A runner who starts behind him, in the fullback's peripheral blind spot while his eyes are on the ball carrier, arrives without being seen, and the fullback's first information about the run is the ball going past him.

The remedies are all uncomfortable. A back three helps, because the wide centre-back owns that channel unambiguously, which is one honest reason so many defensively minded coaches like the shape. Or you assign the ball-side central midfielder to drop into the seam every time the ball goes wide, which is exhausting and leaves the middle thin. Or you accept the risk and defend the cutback instead, which is what most sides actually do without admitting it.

What I would stop hearing is the phrase communication problem. It gets said every time a goal comes from that channel, and it is not really communication. Two players talking to each other cannot resolve a rule that was never written. Somebody at the training ground has to decide, out loud, that in this scenario the fullback goes and the six covers, and then drill it until it is reflex.

Most teams never make the decision. They leave it to be sorted out at full speed, in a stadium, by two tired men who each assumed it was the other one.