Self-defense (in a case of one's capital, not a capital case)

Question

There is a well known rule that if A is threatening B's life, B may kill A, if necessary, to prevent that.

Is there any such rule in non-capital cases? Specifically:

• If A is threatening B with physical injury, can B injure A to prevent it?
• If A is threatening B with monetary harm, can B financially injure A to prevent it?

If so, then:

1. Does B's injury of A have to be proportionate to what A would have otherwise done? For example, if A is seeking to inflict $100's worth of damage on B's possessions, can B, to prevent that, inflict $100's worth of damage on A's? $100.25's worth? $1,000,000's worth? Likewise, if A is seeking to damage B's person to a certain degree (monetary degree in terms of nezek, or to some degree as defined by some other standard), can B damage A to the same degree? to a higher degree?
2. Would B have any liability to A thereafter (in bes din)?

Of course, for practical guidance in any specific case, each person should consult his rabbi; this question is about general rules.

Answer 1

A relevant source (regarding case #2) is Shulchan Aruch, Choshen Mishpat 383:2 (from Bava Kamma 28a). The case is that A's ox has climbed on top of B's ox and is going to kill it. B may pull his ox out, even if this will cause A's ox to fall to its death. On the other hand, he may push off A's ox only if he has no other way to save his own; if he could have saved his ox without killing the other one, he is liable for damages.

Answer 2

The gemara in Sanhedrin 72 says that if a person digs into your house to steal from you, you may kill him. The Rishonim explain that this is because the thief knows that no one lets his money be stolen without a fight, and therefore comes ready to kill the victim if will stop him from stealing. Therefore it is essentially a case where a person comes to kill you, which you may kill him to stop him if that is what is required, or if a monetary solution is available to you, then you have to use that.

However, some of the poskim hold this true only if he actually dug a tunnel, and not any monetary attack.

Answer 3

To complete the answer, regarding #1:

רא"ש בבא קמא, פרק ג סימן יג

וכן שני אנשים נמי מיירי שהתחילו כאחת או אחר זמן אבל אם התחיל האחד השני פטור... ומיהו צריך לומר דאם היה יכול להציל עצמו בחבלה מועטת וחבל בו הרבה חייב...וכן הדין אם אדם רואה שמכין את אביו או בניו או אחיו והכה את המכה כדי להציל קרובו פטור כמו אשה המצלת את בעלה אם אינה יכולה להציל על ידי דבר אחר. וכן אם רואה אדם שישראל מכה את חבירו ואין יכול להציל אם לא שיכה את המכה אע"פ שאין מכהו מכת נפש מותר להכות המכה לאפרושי מאיסורא

Ras"h Bava Kama, 3:13

Also, two people that fight each other, we say the same [like bulls that damages each other - both have to pay for damage] if they started to fight simultaneously or near-simultaneously , but if one started, the other does not need to pay for damage...although, if he could save himself by causing little damage, and he caused massive damage he have to pay...And that is also the rule when one sees his father, his sons or brothers beaten, and he attack the aggressor, he does not have to pay, like a woman that saves her husband [by attacking the aggressor groin], if she can't help him by other action. Same goes for if one sees a jew beat another jew, if he can save only by beating the aggressor, although the aggressor is not risking the victim's life, he can hit the aggressor to save him from sin