In Jesus’ time, being struck with the back of the hand was more an insult than an overt act of violence. It was done to slaves, children, and women. Only the right hand was used. Turning the left cheek to the accuser required them to either relate to you as an equal or break social law. This is non-violent resistance. It requires “a strength of character ready to be tested in the stream of the world.” (Eberhard Arnold)
Remain in the truth even when under attack. Resist evil with love and integrity. Remain holy, just as God is holy. (God cannot be otherwise.) Gandhi did it. MLK did it. Jesus did it. So can you. Losing your composure discredits your cause.