Maybe at your place. Anyone who knows horses and handles them enough realizes that a boot to the belly is an attention getter and nothing more. Just how do you suggest a 110 pound person respond to an 1100 pound horse attempting to kick at a horse walking by? Say "no no".
I find a boot to the belly (if I am on the ground) and a QUIT is very effective. Had the second horse been loose instead of being led by a person, they would of turned to each other and booted each other.
Well, then it's a good thing you aren't a boarder here because you wouldn't stay here. I choose to not allow that kind of thing here, and I enforce it.
I find ground manners training to be effective and if a horse has an issue like wanting to kick at another horse, a few minutes ground work can generally fix the problem.
We are very low key here, have very few problems with our horses and no one here chews on ears, kicks bellies, screams or otherwise loses it with the horses. We do ask each other for help when things aren't going well and frequently, a different hand and different person handling the horse makes the issue just disappear. We've learned that our frustration communicates to the horses and a new person who isn't frustrated can frequently accomplish what the original person could not.
We're not afraid to use a crop or whip when needed, but again, very minimal physical agression is usually needed.
I have a tip for you though, if you think YOU a 110 lb human are going to out muscle or out physical an 1100 lb horse, I suggest you check your meds 'cos you're delusional. LOL! That's meant as a joke, not as a slam, btw.