I kind of understand the idea that elementary students are this fierce or intense because I used to play volleyball during my elementary and high school days, and compared to what I am now, I was definitely more passionate as a child.
Also Togashi's right, the idea is they had a goal in mind, and that is to become a pro, but the actions they are showing are leading them to a totally different path from their goal. I understand why he's irritated with them because, as a reader, I also felt frustrated.