In "Black Panther", Erik Killmonger comes to Wakanda and challenges T'Challa (now the King / Black Panther) for a fight for a claim to the throne, which T'Challa accepts.
The fight is supposed to be a fair fight, and Okoye prevents the rest of the Dora Milaje from stepping in during the fight, saying "there is nothing we can do". In a later scene, M'Baku even asks the Wakandans whether it was a fair fight, to which they reply yes.
But we see that in the middle of the fight, before Killmonger defeats T'Challa,
He impales and kills Zuri during the fight.
And
throws T'Challa over a waterfall without asking him whether he wanted to yield first, like T'Challa had done with M'Baku.
I don't understand how this is a fair fight, and why it didn't get stopped.
Imagine a Floyd Mayweather Jr. vs. Conor McGregor fight. If one of the boxers had stepped out the ring during the fight and punched a random stranger or someone's uncle, I highly doubt they would have been allowed to continue the boxing match, or let off lightly without being charged with assault or something similar.
So why was Killmonger's killing a third-party during the fight considered natural and OK?