While I applaud your willingness to help someone in distress, your story is a good illustration of the fact that situations are not always what they initially appear to be. The screams could have been because of an assault, but they could also have been because of a domestic situation, and they turned out to be a protest of a legal action.
Domestic disputes are difficult even for LEOs. If an assault, domestic or otherwise, had been in progress, what would you have done arriving on the scene unarmed and "out of shape for physical combat?"
The situation you described sounds like an ideal time to call 911 and be a good witness. Inserting yourself into a situation you know nothing about is a practice that has multiple ways of blowing up in your face.