Thanks Jack, for giving an account of your perspective. You are addressing four different things and I will comment on each one. Even if they are related, they each deserve a discussion and unpacking of their own.
1. Approach to finding the definition
This deals with:
What is a word?
Answer: A single unit of speech or text representing a specific concept.
What is a definition?
Answer: The meaning of a word to a group of language users.
What do we derive a definition from?
Answer: We look at language use, and extract the meaning of the word, from how it is used.
You keep confusing the meaning of a word, with a concept that we can outline pragmatically by its inherent properties. Those are two different pursuits. For an example, you keep confusing what I have referred to as hard lines, with the reasons for language use. Those two are related but not the same. You keep listing properties such as “fancy movement”, “feet in contact with the ground”, “hopping”, “fancy running” etc. Those are all properties that you can identify, but they are not evidence of language use, which is what you should be looking for if you wish to find a definition.
The reason why looking for hard lines does not work is because we can have two cases made of IDENTICAL properties, that will be referred to by different terms. There are feats of rhythmic gymnastics, cardistry, freestyle soccer, yoyo, and many other things, that are examples of activities where you can find an identical move in juggling, yet it will not be referred to as juggling.
2. Default form
There is no sport of sports, no dance of dancing, no game of games, no sculpting of sculpting, no painting of painting. So if I ask a connoisseur of each of those to teach me to do sport/dance/sculpt/paint, there is no standard, there is no DEFAULT that most everyone will bring up. Juggling is different here (perhaps even unique?) that we have a default, in many more ways than one. The first thing you are taught, the base that you learn tricks from, the pattern with least components (mirrored versions of one identical type of throw), and maybe even the oldest trace (Beni Hassan, Egypt).
Just because juggling happens to have a default form does not mean it should be part of the definition of juggling, that is a different question.
3. Definition truth
The problem that we are facing is that we can not define juggling by hard lines, such as throwing, catching, balancing, etc. because identical things will be referred to as different things, depending on the cultural context that they exist in. So how do we deal with that?
The truth is, that juggling is a set of activities, that have increased and decreased in number, throughout history. The activities have their root in entertaining, you could say that from the beginning juggling meant “entertaining” and slowly moved to mean “things by which you entertain”, and then yet a bit later, those things by which you entertain were further specified. That set of activities was slowly more and more distinguished, and a culture came to exist around it. Things that were related in one way or the other, to any of the things in that set, as well as existing in the culture that surrounded said activities, were referred to as juggling. For some reason, one of the activities in the set got a central role: Cyclic throwing and catching more objects than the amount of hands. That activity became known as juggling, and from there on, both the set of activities and that specific activity became referred to by the same term “juggling”. That is the truth and what do we make of it?
4. Definition conclusion/proposal
To say that the set of activities known as juggling is defined by a relationship to the default form, plus a cultural context is a proposal. The actual, causal truth is listed in 3.
The truth listed in #3 results in #4. If you can make a better conclusion of #3 than default form+cultural context, I am happy to discuss it. I have seen ZERO arguments against #1,2,3 since I started talking about the definition. Only people who are confused by what a definition is, what a word is, and what juggling has and is. If you wish to discuss any of the 4 points, please refer clearly to which one you are addressing.