Well, the whole stuff in the sermon on the mount that's already been quoted to you seems to rule out self-defence. But beyond that, given that Christianity is essentially about being selfless, I'm not entirely sure that defending oneself can really be said to sit well with that. I'm not even talking about killing in self-defence (which raises all sorts of ethical issues of its own - if taking a life is an act of evil, can it suddenly become an act of good if it's done in "self-defence"? If so, why and how?), but just self-defence in general. As Christians (I realise this isn't a Christians-only section of the forum, but I'm writing from a Christian perspective), we're called to take up our cross and follow Jesus, and that path involves suffering. As long as we're faithful to Jesus, should we do things to prevent ourselves from suffering at the hands of others, physically or otherwise? Human instinct says "yes," but that seems to be a case of human instinct not squaring with Jesus's expectations of us.