We find the most basic statement about self defense in Exodus 22:2. If a thief be found breaking up [i.e. breaking in], and be smitten that he die, there shall no blood be shed for him. In other words, a man defending his home is not held guilty of murder if the perpetrator dies. That's God's standard for self defense.
Some people complicate the matter by trying to set the Bible against itself. For example, "Thou shalt not kill." (Exodus 20:13) does not mean no killing under any circumstance whatsoever (as some pacifists assert). If this were the case, then we should not swat flies, slap mosquitoes or even use antiseptics, which kill bacteria. An investigation of the greater context as well as the Hebrew word used, reveals that the meaning is "Thou shalt not murder."
Similarly, Jesus' admonition to turn the other cheek (Luke 6:29) is often used to promote pacifism. It would take too much space to go into an explanation of this passage's context & its relation to the lex talionis of Biblical Law, so for now suffice it to say there is a big difference between someone's slapping your cheek and someone else's trying to cave your head in with a baseball bat.