From my experience, school sports in Australia are nothing compared to what they are in the States. They seem to reach a kind of scary, cult-like status over there (or, at least, that's what I've gleaned from binging American teen dramas), but here, it's a lot more casual.
Generally, you start in primary school with either soccer or netball, then in high school you might take an interest in something else — rugby, basketball, etc. But unless you go to a fancy, private school, it's unlikely you even have an official school sports team.
When it comes to heatstroke, I think there are legit rules in place where, if it reaches over a certain temperature, schools have to send everyone home? But I don't know if that's just an old wive's tale. I hope not.