It does happen, but as you well know all it takes is one. You also know that a Street fight is very unpredictable and very dangerous especially a fight between 2 strangers as neither one knows the others motives.
But as someone who has training, if a person is attacking you , do you simply let them go at it because they are untrained and "probably" wont hurt you? Or do you defend your self with every tool at your disposal?