Below are a few verses that touch upon the subject of self-defense or defending another.
There are more verses, but these give an overview of the topic.
Genesis 9:5-6 (ESV)
5 And for your lifeblood I will require a reckoning: from every beast I will require it and from man. From his fellow man I will require a reckoning for the life of man.
6 “Whoever sheds the blood of man, by man shall his blood be shed, for God made man in his own image.