They do both. Do more research, you are making yourself look foolish.
I truly hope you are not a coach, or worse, take peoples money by "training" kids to throw weighted balls as far as they can. There is no such thing as "making yourself look foolish" when you are putting health in top priority, unlike yourself. Foolish is having to explain to people why you did such foolish things in trying to "help" their kid throw with more velocity, when their kid's arms are hanging off their bodies... All torn up. Once again, I read a Tom House interview, and even heard it first hand from he, in the video YOU posted, he does not have players release the weighted balls. They are strictly mean for developing arm strength and muscle. Please, for the love of all that is good with mankind, tell me you do not allow kids to actually throw weighted balls to each other, much less have long toss with them. PLEASE tell me this is not happening under your supervision.