Had the bully not been hurt...not only would he have beat the kids ass but he would have continued to bully the kid - that I have no doubt in my mind.

I have doubt. When I was in school I was bullied by a couple of kids, and one day I just said fuck it and got into a fight, and lost. A couple of days later, more bullying, new fight, lost again. There may have been a third fight, I don't really recall, but even though I never actually won a fight, just being willing to put up a fight was apparently enough to make that particular bully leave me alone. Bullying is rarely something personal and if there is someone easier to bully most bullies will take the path of least resistance.