In the days before compulsory elimination, I had a horse rocking gently back and forth, back and forth, on my fence before it managed to scramble off, by some magic means imperceptible to me as Fence Judge, and continued on its merry way. I gave penalties for a “fall” because it most certainly had lost all forward momentum! The TD later strolled up and gently asked me for my reasoning for giving penalties. I explained that the horse had come to a complete halt on the fence - but then added the clincher, quoting one of the favorite sayings of this particular TD, “It is always better to give the penalties and take them off later than add on extra penalties afterwards”.
These days the rules are much clearer so falls are easier to score and, importantly, code into the safety database.