violence is physical (sometimes emotional) pain inflicted on a living being (or beings).
property destruction is usually not considered violence.
some people see a grey area when property destruction is committed against people who are poor (more poor than usual?), as this could be considered bad for people's health (poverty is the biggest health risk, as we all know).
this definition (violence is only against living beings) is ok as far as it goes, but to me it seems to have humanist roots, which i disagree with. but perhaps that is the beginning of another question.