There is nothing more satisfying than a bully biting off more than they can chew. One thing with bullies that rely on physical oppression is that they are not particularly skilled in almost all cases. The skilled ones usually have bigger fish to fry and have been humbled in their respective activities. As such, the only thing backing them up are self confidence of being superior to their victim, which is perpetuated by their victim not proving them otherwise.
In some cases, the victim has more ability in defending themselves, and it is bad news for the bully when the victim is pushed to the retaliation point. After such an event, it’s only natural for the bully to reevaluate his life choices.