Stranger in Danger! Would You Step In to Help?

You are taking a leisurely walk through your neighborhood park and you witness a man who is engaged in a heated fight with his girlfriend and roughly pushes her to the ground. Do you step in and tell him to back off? While watching your young daughter laugh with glee as she flies down the slide by herself for the very first time, you overhear another mother screaming at her son and shaking him violently. Do you get involved to protect the child? At what point do we feel compelled to get involve