Legal curiosity - public violence

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I've been wondering about this for some time, and I wonder what it is like in different areas. The situation: I was riding public transportation, the light rail system (similar to a trolley, only faster and the stops are further apart) I was reading a book, and someone sneaked up behind me and screamed next to my ear, in an obvious attempt to entertain himself by watching me jump. I don't think I did too much, being totally engrossed in the book, but I did read slower paying attention to the sounds around me to make sure the person didn't try any more aggressive funny business without me making direct eye contact. 1) Was a crime committed at this point? 2) If a physical fight followed, does it matter who initiated it, that is, threw the first punch - the original victim or the instigator? It just occurred to me the second question may depend on a jury trial ...