The object of self-defense is to stop aggression and restore peace. This may involve putting your attacker into enough pain that you can create an opening and escape. It is biting and clawing and stomping. It is survival. It is not a sport.
Listen to your instincts. There are bad people and neighborhoods. Mind your own business. Self-defense is lots of attitude and some technique. There is strength in numbers. Using a cell phone, yelling for help, drawing attention to your situation, asking for an escort, calling a taxi, apologizing and giving up the money are effective techniques.
Your confidence is your shield. Only fight if you are physically assaulted. Then, commit completely with the mindset of staying alive. Concentrate on five target areas; eyes, throat, solar plexus, groin, and the arch of the foot. Hit through your target. Keep hitting, and then seize a moment to retreat to a safer place where your options multiply.
Karate began as open-handed fighting because weapons were banned but weapons work and weapons are everywhere. Think before escalating any situation. No matter how tough you think you are, remember that when two tiger fight, one is killed and the other is seriously wounded.