I would try contacting a person who is close to me, especially if I sense any danger. I would also work hard at remaining calm to avoid any irrational actions that may expose me to a more dangerous situation.
Depends upon the situation-if it was a case of a retired coach molesting a child in a shower, I believe MOST people, upon walking in on that scene, would kick the abuser in the ribs to get him off his victim & hustle the kid off to a hospital.I very vocally criticized some elderly man in a hardware store yesterday for calling his wife "f***ing ugly" in front of 5 or 6 strangers. Your common sense/gut feeling SHOULD tell you how to handle a situation. Those brave people who see a car run off the road & into water don't stop to ask someone how to handle the situation-they dive in to help rescue the driver & any passengers at risk.