In the sporting world of gladiators, there were two options for a defeated gladiator: He had to have shown either enough skill or enough cowardice during the battle. Otherwise, he would be killed in the war arena by organisers of the match.
So far, Ruto is a defeated gladiator, but he cannot be killed politically because he has shown great skill in political battles. His soldiers had no option but to accept the 'cut', but gods now demand that he slays them or they be given a golden chance to do the same to him.