Many years ago I was walking through a market when a man started bullying a woman, shouting and swearing and slapping her. Then he punched her in the face knocking her to the ground, and began kicking her. That was the last straw for me, I couldn't believe that people were just standing by watching, even men. I just ran at him and shoved him hard and kept shoving him away from her. Only then did two men grab his arms and hold on to him. I went to help the woman who was bleeding a lot. She then started on me screaming "leave my 'usband alone!" I told her he'd probably broken her nose, she said "So what it's my bloody nose" It most certainly was! A nearby stallholder told me not to bother about her, she liked being his punchbag! Seems it was a regular occurrence.
Another time I intervened to help an elderly lady who was being harassed by to teenage boys. She looked very frightened. One of them said "Yeah, what you going to do then?" I had no idea what I would do but replied "Sure you want to risk finding out?" It was enough to make them think twice and walk away. I walker her home and she was very thankful I had been there.
Would I do either of those things now? I honestly don't know. I was younger then, impulsive, strong and fast on my feet. I'm a lot older now, weaker and slower, but still impulsive. I like to think I would still do something if only make a lot of noise or call the police, I don't think I could stand by and ignore it. I hope I never have to make that decision.