At ancient times, only the right hand was used to beat servants.
"But whoever strikes you on the right cheek..." is a master beating the servant standing behind him, his right hand hitting the right cheek of the servant.
... turn the other to him as well." (Mt 5:38-39)
This means that if you have been beaten, turn around and face the opressor.
Protecting oneself with force is a Christian thing to do.
If men fight and hit a pregnant woman and her child is born prematurely, but there is no serious injury, he will surely be punished in accordance with what the womans husband demands of him, and he will pay what the court decides. But if there is serious injury, then you will give a life for a life, eye for eye, tooth for tooth, hand for hand, foot for foot, burn for burn, wound for wound, bruise for bruise."What's being referred to by the Lord is between two freemen and was regarded as an insult. The Lord is saying that we shouldn't return insults. He isn't saying that we should allow ourselves to be seriously injured or killed; a slap to the cheek doesn't do that.
If a man strikes the eye of his male servant or his female servant so that he destroys it, he will let the servant go free as compensation for the eye. If he knocks out the tooth of his male servant or his female servant, he will let the servant go free as compensation for the tooth."-Exodus 21:22-27