Every theory is underdetermined by the data. This means that any set of data can prove multiple theories. In fact there will always be more than one theory that is supported by the data, no matter how much data you collect. Underdetermination means that there is some determination by the data but not enough to exclude all other theories. Underdetermination does not mean that no theories are excluded. In fact, most of the time many theories are excluded. It is just that there will always be other theories that are also supported by the data besides your theory.
This is important for football in the following way. When an analyst does opposition analysis for an upcoming match for instance, that is in fact a theory that he is trying to substantiate with data. So if an analyst comes up with only a single prediction of what is going to happen, he misses that the same set of data substantiates multiple theories. It would be much better if the analyst would describe several possible scenarios for the upcoming match with his probability estimation for each scenario. And if he would add the scenarios that he would exclude based on the data he collected. Or, if he can’t rule them out completely, at least describe which scenarios he finds very unlikely to happen coupled with the low probability estimations for those unlikely scenarios.
The same goes for scouts. No matter how much data a scout collects or how many video or live impressions he gets from the player (which is data in another format), there will always be multiple theories supported by this data. Data can exclude a player of being a viable option for the club because the chance of success is too low. But data (which includes impressions by the scouts themselves) can never absolutely guarantee that a player will be a success at the club. This has not only to do with a lack of data or human errors, but even if the club would have infaillible scouts and a perfect data set (which is impossible), even then every theory would still be underdetermined by the data. So also with scouting reports for players that have a high chance of success with the club, the scout already has to indicate what plan B would be if the player turns out to be less of a success than foreseen.