On the legal side of things, I sat in on a talk about liabilty (not about P-ball specifically, but it applies anyway).
If you, the site, have provided all the necessary safety equipment and have showed them how to use it and why. When they still purposefully remove that safety equipment, they are subject to contributory negligence, in other words, its their own damn fault, they are adults and are aware of the risks they are taking in removing the goggles, depsite your warnings. SO if they tried to sue, they should not be successful.
If the goggles fell off due to being faulty or badly maintained, then the site would be screwed!
Anyway, sounds like you did exactly the right thing, and Robins advice about holding them down with the goggles in place would be justified if you are able to do it safely, ie, you are big enough to pin them without struggling.
Also the self defence single strike should be ok, but it might not do the site rep too good and you may have to do the whole court hearing thing, which would be a pain in the ass, but maybe worth it
