Surf Etiquette: Snowballing

I went out surfing a few weeks back in a lineup full of beginners who were blowing their waves over and over again. It was in sloppy small surf so the stakes were minimal. Surfing etiquette was kind of non-existent that day. Here's what I was doing in the lineup that made me realize I was practicing bad etiquette. I would go for a wave along with two or three beginners and I would watch the beginners closest to the curl to see if they made the wave and, if they blew it, I would then follow through with my takeoff. However, there were times when those other surfers closer to the curl were actually competent surfers. When those surfers came toward me I would pull out of the wave, but I realized I was snowballing their wave. I could clearly see that my pull-backs from the waves were technically not a drop-in, but were nevertheless destroying the section of the wave the competent rider was on. So, I came up with my own snowballing rule: always assume the rider with priority is competent and don't even get in a position that will start a snowball. The question is, however, should you follow this rule in a free-for-all beginners surfing scrum where surfing etiquette doesn't apply? If anybody has other insights into the finer points of avoiding being the cause of a snowball to other surfers, I'd love to hear them. For example, when a wave is breaking left and right, can you assume that a rider is going to go in a direction that allows the other surfer in position to go in the opposite direction?
What is snowballing? See following video.
What is snowballing? See following video.