actions and obligations of a landlord

[sthrngent]

What is the name of your state? Virginia

I had a written lease to rent a room in a private home. Due to many problems with a dangerous and violent tenant who rented an adjacent room, my landlord offered to reduce a month's rent by 200 dollars. I paid the reduced amount only to have her inform me three weeks later she had reconsidered and now was demanding the balance be returned. I declined to do so and moved when my lease expired. She now is withholding the amount from my security deposit for the claim of "back rent". Does she have any legal grounds to do this ? Also, what obligations does a landlord have to ensure a tenant will live in a reasonable and civilized manner and not harrass or threaten other tenants and generally abide by the rules ? The problems this other tenant caused simply are too numerous to list and the landlord refused to accept any responsibility or follow the proper procedures for an eviction.
Thanks for any responses.

[Alaska landlord]

Don’t know about your landlord, but since I don’t like tenant wars and hate having to determine who the victim is, I would have given both groups notice. As far as the payment issue, do you have anything on paper stating that she was giving you a reduction in your rent?

[Cvillecpm]

You should have gotten the offer of $200 reduction in writing or documented it on your check for the balance....otherwise, sue her in Small Claims court for your deposit balance.

[sthrngent]

Well just to be clear, there was no "tenant war" as Alaskalandlord called it. Other than threatening and harassing me on several occasions the problems with this tenant were independent of anyone occupying the second room. He smoked and drank when neither were permitted, tore an outside door from its hinges in a drunken rage and ruined the entire door frame in the process, used vulgar language audible to a young girl upstairs, and would leave full bags of groceries in the middle of the floor to melt, rot, and spoil.
I guess I should have had her put it in writing, but as I enjoyed good relations with her and she offered the reduction (I did not initiate that), it just never occurred it would come up again. But thank you both for your views.