HMG's current security classification system - which applies to govt departments, govt agencies, contractors to etc etc and, one would hope, even to Stafford Borough Council, provided that the concept of 'government' can be stretched that far - defines information which should be marked SECRET broadly as follows:
'SECRET
Very sensitive information that justifies heightened protective measures to defend against determined and highly capable threat actors. For example, where compromise could seriously damage military capabilities, international relations or the investigation of serious organised crime.'
It is quite hard to imagine what, other than ignorance of the above and of its precursors, would have led some council official in Stafford to have decided that information relating to a planning application for a hockey pitch on privately-owned land in Stafford could fall into that category.
It is just about conceivable that some reference may have been made, somewhere in the documents so classified, to the provision of strategically-sensitive sporting facilities for the inhabitants of the local military base, or possibly to the existence of hitherto unknown top secret nuclear bunkers, mysteriously still in use only in Stafford, underneath a football pitch somewhere, or, carelessly, to the fact that somebody's relative who works at the police station heard once that him who lives near the hockey pitch is a seriously organised criminal and the rozzers want to make sure they can carry on getting overtime for sitting in a car up the road dreaming of appearing on Cop TV. If so, then there may have been grounds for redaction of the documents. But the original security marking would appear to have been not remotely justified.
It is more likely to have resulted from genuine but innocent incompetence, which has now been rectified.
Or, this being Stafford, some local person of infuence with fingers in pies put the frighteners on somebody in the council, and an over-reaction ensued.
But the more worrying possibility is that, as suggested upthread, there is some perceived conflict in this matter between the commercial interests of SBC, or of somebody connected to the latter, and those of the hockey club. And that if that is what informed the initial, apparently ridiculous, security marking, then that action looks very like misconduct in public office.
And as we all know, that sort of thing could never happen in Stafford.
Have you spoken to your MP, or thought about a FOI request to the council asking for background information? These are your rights under law.
I should add that, with the exception of the quote from the published official guide to HMG's security classification system, all of the above is entirely speculative, mostly facetious, and is not intended to suggest any wrongdoing, irregularity, misconduct or inappropriate influence on the part of any category of person whatsoever. All is for the best in the best of all possible worlds.