The Bible & Self Defense

(Matthew 5:38-39) “You have heard that it was said, ‘An eye for an eye and a tooth for a tooth.’
39 But I tell you not to resist an evil person. But whoever slaps you on your right cheek, turn the other to him also.

Do Christians have any Biblical support for self defense? How can we reconcile the idea of self defense with Jesus' teaching about "turning the other cheek" and loving our enemies?

(Matthew 5:43-44) “You have heard that it was said, ‘You shall love your neighbor and hate your enemy.’
44 But I say to you, love your enemies, bless those who curse you, do good to those who hate you, and pray for those who spitefully use you and persecute you,

When I was a child, I believed that these texts meant I should not fight back against an attacker. I was in the fourth grade and had a "friend," Greg, who was a spoiled bully. At the bus stop after school one day, Greg attacked me. My books and papers were scattered on the ground and Greg was sitting on my stomach pounding on me as I tried to protect my face from his blows.

My sister, Cindy, who was two years younger than I, did not have my religious compunction for pacifism. Coming upon this scene, she yelled like a viking warrior in curls and swung her metal lunch box like a medieval mace. Greg looked up just in time to catch the lunchbox with his nose, which began bleeding immediately.

Greg ran off. I was mortified. Taking a beating was (at least in my mind) my Christian duty, but my little sister had interfered! She came to my rescue and defended me with force. She saved my bacon, but damaged my pride and contradicted my simple Christian philosophy.

What should I have done?

Tell me what you think and I will continue this thought in a few days.