Legal action against threatening tenants?

[Mark Hu]

I recently was threatened with harassment by a tenant. I felt angry and helpless, since laws here in California are so slanted towards tenants that I was not certain I could do anything.
What legal remedies are available? And what about physical threats? I nearly got in a fistfight with a tenant 3 years ago. What legal remedies are available to a landlord threatened with physical violence, which will not clash with tenant rights?
I find there are relatively few crazy tenants, but they do crop up regularly...