If we witness a person harming others and nonviolent verbal intervention fails what would God have us do?

​One of the repeated characteristics of God in the Bible is his concern for the weak and helpless, and his direction to us that we share that concern.  The government is given the ordinary responsibility of protecting its citizens from harm and restraining evil, for which purpose they are said to “bear the sword,” but in cases where we witness one person doing harm to another the sixth commandment gives us the right and responsibility, according to God’s law, to defend the life of another using any means at our disposal. 
The Bible is also clear that this concern for the protection of innocents and the legitimate concern for true justice does not extend to our seeking vengeance for wrongs done to us or others.