Self-defense
Self-defense (also: self-defence) or private defence is a countermeasure that involves defending oneself, one's property or the well-being of another from physical harm. The use of the right of self-defense as a legal justification for the use of force in times of danger is available in many jurisdictions, but the interpretation varies widely. To be acquitted of any kind of physical harm-related crime (such as assault and battery and homicide) using the self-defense justification, one must prove legal provocation, meaning that one must prove that they were in a position where not using self-defense would most likely lead to death, serious injuries and property damage.
Buddhism is emphatically nonviolent (ahimsa) and does not allow killing of any kind (except the "killing" of anger). Many Buddhists (but not all) are vegetarian and the Buddha's teachings clearly include all sentient beings, which thus, prohibits hunting and fishing.
But the issue of self-defense does not come up too much in the Tipitaka and in regard to the general view of ahimsa, it is not so easy to find a clear answer on if self-defense is allowable.
Implied references
There are a few implied references in the Suttas / Tipitaka.
The Buddha was not an anarchist. He regularly met with kings and taught them. He supported the idea and need for governments. As such they would need to defend themselves from time to time no matter how peaceful they are; the neighboring kingdoms may not be so peaceful or Dhammic.
"A king should never fall into the power of anger. Rather, let him control his anger, for neither a person’s interests or duty thrive when one is angry... When a dispute arises, he should pay equal attention to both parties, hear the arguments of each and then decide according to what is right. He should not act out of favouritism, hatred, fear or foolishness, but should hear the arguments of both sides and then decide according to what is right... While keeping an eye on state affairs, a king should dispense happiness to all. He should prevent all from committing violence and show that it is righteousness which brings reward. As in the days of former kings, large numbers of immigrants came together to be admitted into the realm, so should you admit them. Always show favour to the poor but also protect the rich who are your subjects...Do not foster hostility towards neighbouring kings. Whoever hates, will be repaid with hatred by his enemies. Cultivate ties of friendship with your neighbours, for others honour those who are steadfast in friendship. Do not talk at great length on all sorts of subjects, but give your judgement at the appropriate time and keep it to the point...Always protect those who live justly. For the wheel of power turns in dependence on the wheel of justice...Do not appoint as headmen of villages or provinces even your own sons or brothers if they are unscrupulous, violent or base...A foolish or greedy minister is of no value to either ruler or realm. Therefore, appoint as your ministers men who are not greedy but prudent and devoted in counsel and who can guide the realm. Your eyes are not as good as those of an informer, nor is your policy. Therefore, you should employ an informer in all your affairs." Tesakuṇa Jātaka from the Jātaka (Ja.V.109)
The quote above includes "Always protect those who live justly" which could imply self-defense of oneself and / or others.
In the Mahaparinibbana Sutta the Buddha talks about conditions for a nation's success:
"What have you heard, Ananda: do the Vajjis duly protect and guard the arahats, so that those who have not come to the realm yet might do so, and those who have already come might live there in peace?"
"I have heard, Lord, that they do."
"So long, Ananda, as this is the case, the growth of the Vajjis is to be expected, not their decline." (Digha Nikaya 16)
Specific reference
There may be only this one specific reference which appears to directly allow self-defense:
In the Vinaya, Suttavibhanga, the 92 pacittiya (rules entailing confession), number 74 states:
74. Should any bhikkhu, angered and displeased, give a blow to (another) bhikkhu, it is to be confessed.
The factors for the full offense here are three.
- 1) Object: another bhikkhu.
- 2) Effort: One gives him a blow
- 3) Intention: out of anger.
Non-offenses: According to the Vibhaṅga, there is no offense for a bhikkhu who, trapped in a difficult situation, gives a blow "desiring freedom." The Commentary's discussion of this point shows that it includes what we at present would call self-defense; and the K/Commentary's analysis of the factors of the offense here shows that even if anger or displeasure arises in one's mind in cases like this, there is no penalty.
Summary: Giving a blow to another bhikkhu when impelled by anger, except in self-defense, is a pācittiya offense.
And another important point to the above is that that is the rule for monks. How much more leeway might lay people have? Not to kill of course, but certainly protect for self-defense.