Players should own the numbers their legs produce

Wearable output has quietly become contract evidence, and almost nobody in the dressing room controls the file.

A footballer signs for a club and, somewhere in the paperwork, agrees to wear a vest. The vest logs accelerations, decelerations, distance in speed bands, and increasingly limb-level load from sensors nearer the ankle. Over a season that becomes a very detailed portrait of a body. The player generated every byte of it. In most arrangements he does not own a single one.

This has stopped being an abstract point. That file follows a transfer negotiation now. A buying club's medical staff will ask for load history, and a declining top speed at twenty nine, or a pattern of asymmetric decelerations after an old ankle problem, will move a fee or kill a deal. The player is being valued on evidence he cannot see, cannot check for error, and cannot take with him when he leaves.

And the error is real. Anyone who has worked with these systems knows the units drift, the placement of the pod changes the readings, and comparing one manufacturer's high speed band to another's is not straightforward. A club changing supplier can produce a step change in a player's apparent output that has nothing to do with his legs. If that artefact ends up as a footnote in a scouting report, nobody involved will ever know it was an artefact.

The fix is not complicated. Give the athlete a copy in a portable format, as a matter of course, the way a patient can request a medical record. Let him carry it to the next employer and to his own independent physio. Some player unions have started pushing on exactly this and they are right to.

The counter argument from clubs is that the data is a competitive asset, that they paid for the kit and the analysts, and that the raw stream is meaningless without their models. The first half of that is fair. The second half is an argument for sharing the raw stream, not for withholding it.

What worries me most is the drift towards insurance and contract clauses keyed to load numbers. Once a bonus or a renewal depends on a threshold, the incentive to shade a training session, or to quietly not wear the pod on a heavy day, arrives immediately. Measurement changes behaviour. It always has.

The vest is fine. The ownership is not.