As any horseperson with a shred of common sense knows, drivers do not kick any horse in the hocks.
"Kicking" actually means letting their foot out of the stirrup and letting it hit the horse in the meaty area of the flank/upper rear leg. This does far less harm than hitting an animal with a whip-matter of fact it causes zero pain to the animal.
Bettors need to be informed of this fact. Now, if a horse bites or steps on you in the barn and you kick one in the belly, that might hurt a little, but not nearly as much as the horse biting or stepping on you. In the case of Amy or myself, we would probably fall over backwards when attempting this, giving everyone else in the barn a hearty laugh.