To prevent the situation from becoming violent you’d first separate the two parties so one can cool off. While the new student is somewhere else calming down speak to your friends why they are spreading these rumors and explain how it’s making the new student feel. If they refuse to listen or acknowledge fault and apologize go speak to the new student and tell them it’s best to get a higher authority involved. Such as a teacher, dean, professor, principal, etc to help assess and settle the situation to help prevent it from escalating more than it has to.
Hope this helps :)