Please help me

ok i have a debate tournament coming up. the topic is if it is just for a victim to respond to repeated domestic violence with deadly force. i have the negative down but the affirmative is a little harder. i need an example of a case in which it was allright to respond with violence. i have looked but i still have not found literature that states this, can someone help me support my affirmative case?
my value and criterion is justice and individual rights