I think that, in terms of "required elements", slapstick only really needs exaggeration and make-believe in order to qualify as slapstick. As far as physical and violent, verbal slapstick (such as the infamous quips of Groucho Marx) is very much a thing--though the argument can be made that verbal abuse is violent in and of itself. I feel that "ritualistic" is a misnomer here, and "formulaic" may be a better choice. But even so, that's not a required element in my opinion.
It's the exaggeration and make believe aspects that separate slapstick from outright violence and cruelty. The sound effects, physical actions, and facial expressions are all exaggerated to where we know that what's happening isn't real, and it makes it okay to laugh at this scenario. Without these elements, we're just watching outright violence and have entered a grey area where it's only funny if it is not cruel.
