By sending him to prison

"This is embarrassing," Headmistress Cai looked at Yin Rentian. As Yin Fu was the victim in this scenario she did not say anything to him. What was more Yin Fu was the top scorer and his attitude and behaviour were perfect at the academy like a perfectionist. 

On the other hand, Yin Rentian was like a mad dog who bit and hit anyone whom he found unsettling or was unhappy with. Thus, she knew it without even seeing the surveillance recording which she did just to give Yin Rentian the benefit of her doubt and sure enough it was Yin Rentian who started the fight.

"You are not kids, Rentian. You cannot kick or punch someone just because you find them doing something that you do not like! You are a law student so behave like one!" Headmistress Cai felt like suspending this mer once more but she did not want another decapitated head in front of her house.