My son got into an argument with another tenant and landlord told him to leave by 1st of the month but other tenant can stay. Is this legal?

If he's evicting him he'll need to do it in line with the local laws. What state is your son in? And was it just an argument? Or was there more to it than that?

State is ky---she spit on my son , he spit back and she shoved his head in a window

Unless she files charges for assault and gets him arrested and convicted, she has to evict him according to the laws of the state.
What does she claim your son did that would provoke spitting? The fact that he spit back doesn't show any more maturity than she did, so I wouldn't help him too much. He needs to work on acting like an adult.

Lets get some more facts here. Are both your son and the other tenant living in separate units of an apartment building? Or are they roommates? Does your son have a lease? Were the police called for this incident? Is there a police report?

The landlord has to give at least a 14 day written notice to vacate in KY. Also, there would have to be a provision in the lease that prohibits illegal activity (assault is an illegal activity).

As long as the landlord complies with the terms of the lease and the law, the LL has the right to terminate your son's lease and not the other tenant's.

Tenant Services & Housing Counseling, Inc.
200 E. Main St.
Lexington, KY 40507
(859) 258-3960

Louisville Tenants' Union, Inc.
425 W. Muhammad Ali Blvd.
Louisville, KY 40202
(502) 587-0287

Maybe these places can help