Legal to install camera facing front gate?

[Rao Venugopal]

I live in a duplex in San Francisco.  In the building on the ground floor there is a pathway which leads to the stairs and a shared garage.  I live in the second floor and my neighbor lives on the second floor.

I have not been getting along with my my downstairs neighbors and they have recently been getting very passive aggressive and trying to provoke us.  They scream at us in vulgar language, use threatening language and posturing towards us in the common area and do not maintain the mandated social distance.  My landlord has take a hands off approach to this whole issue.

Today the male neighbor threw garbage at my wife (which did not strike her) when I was in the garage and she was in the aforementioned ground floor pathway.  My question is, what are my options?  I would like to collect evidence of said behavior so that I can present it as evidence to cops but don't know if it is legal if I install a camera facing the front gate of the duplex.  Please advise.

Thanks

Rao