From the reaction from their own side, it seems like they think that she is big enough of a threat to eliminate early before she grows stronger in the future. If successful, they might disqualified 1 person for 1 death, but they get rid of the "growth" character who is like to be young enough to qualify for future tournaments that the attacker no longer can join.
Yes, but after they started attacking the beast master, shouldn't the tournament staff or whatever been immediately enforcing the rules, trying to break up the fight, and disqualifying the offending combatant? Or calling out a warning? But they did nothing and no one even reacted to the rules being broken. They made it seem like the rules are only enforced
after the battle is over.
If I was watching a boxing match, and someone clearly violated the rules by pulling out a sword all of a sudden and swinging it, at least someone should have reacted. Maybe no one would go into the ring to break up the fight because it is a sword and the staff wasn't expecting to defend against a sword, but there might be screams from the audience, whistles being blown, maybe someone retreating from the ring...