@Long:
Primitive societies arent always the most logical. Cruel rules that lack consistency were a hallmark of medieval religious rules so all the hullabaloo about punctuality and the no outside intereference allowed but dont forget your opponent made general sense to me
I'm no expert on anthropology but I don't think the tribe is big enough for us to see those kind of rules.
It is assumed that individuals can keep about 150 relationships (https://en.wikipedia.org/wiki/Dunbar%27s_number )
There are 40 in the village (altough I'm unsure about Kohaku's comentary in that scene, so we can say there's maybe a dozen more elders and childs; this is from chapter 17, btw). Everyone knows everyone. Tribes this small work more a like family/clan.
You can certainly have disagreements and strict rules in families and clans but it is also much easier to speak up and find a common ground if those situations aren't hurting other tribe members.
And this is not a religious event, which could indeed give a reasonable justification for the rules, it's a sort of social contract and those change more easily.
But after reviewing the scene I got a different reading, tbh.
The look on the referee's face, who is related to Ruri and the management of the tribe, iirc, gives me the impression that it was more of a concious decison to let such antics fly, given that from their prespective Magma is the best candidate.
If such thing is presented in the future chapters I'll have no problems with how that chapter went but if that's not the case I'll keep calling it bullshit.