All things being equal, a man will almost always, if not always, defeat a woman in a physical confrontation. So, what to do if you're a woman with no one to help you?
All things are not always equal. Sometimes a man will be bigger, but possess no fight skills. That's where some self-defense classes could come in handy.
If I may... I recommend Systema. Check it out.
I'd recommend this over the popular Krav Maga, because it's more relaxed and doesn't rely on brute strength. I also like Jeet Kune Do (JKD), but I've learned that Systema is better for multiple attackers -- unless you're
really good at JKD.