'defend'? of course, but it all depends on your own abilities right. I mean if you are smaller or they have a weapon of some sort then you may need to use more force to protect yourself, which may not be enough but as long as you try.
I've always been a fan of aikido because it is all about re-channeling energy, using someones momentum to get them to the ground and in a position where they can't hurt you, themselves or anyone else. Protecting yourself while focusing on the attackers safety. Some people like teh idea of making attackers hurt or die etc but a lot of them may not be in a stable mind-frame, for all you know it could be out of character for them and helping them may be what is needed. really depends but I do generally like the idea of defending without causing any unnecessary pain/conflict, can be counter-productive.
https://en.wikipedia.org/wiki/Aikido