I chuckled when I read your line "And among adults, this sort of refereeing shouldn't be necessary." My first reaction to the story was "grow up!" (no, I don't know how to do italics or bold either ;-))

The anti bullying training I've received really drove home that the critical actors are the bystanders. A single person speaking for civility can often break the chain. As MLK said, “In the end, we will remember not the words of our enemies, but the silence of our friends“ If a bully isn't resisted--either by the victim or bystanders, they will continue because the activity leaves them with a sense of vindication.

But to do this--to stop the dog piling--takes bravery--peer support can help that.