I think that depends on where you live. Like the post above yours, these bullies travel in packs. And even if your kids has MMA or Boxing ability odds are highly likely - nowadays — that it’ll get turned around on your kid that they said or did something to provoke the bullying. All one of those kids has to do is claim they were called a name and your kid gets branded.
And even if you did defend yourself, these gangs will keep coming, probably with weapons.
This is how it is in most cities in 2008 America.
My youngest is in a high school where there are several gangs. They don’t mess with him for two reasons. He’s a nice guy who treats everyone with respect and he’ll knock your teeth out if you mess with him in the wrong way.