Greetings @ALEXANDRIAN
PP-Stalling is very subjective and depends 100% on the course of the match, as it can be used as a tool to achieve victory. Generally, PP-Stalling becomes illegal when its used to extend unnecessarely the length of the match, this can be explained in the following example:
Of course, this case also depends on the state of the match as your last pokemon could also be able to achieve victory if your opponent's team cannot deal with it or are wore down during the match. To put it in simple terms, when the PP-Stall is used to simply flex, annoy and extend the length of the match without a clear reason (Win condition for example) it can lead to harsh punishments as told in our Public Punishment Policy. Thats why we require video evidence, ideally from the entire match to allow us to judge properly whether PP-Stall/Switch-Stall was used as a win condition or unnecessarely.
Novus's post in Need staff member to explain pvp rule was marked as the answer