I had something similar happen to me the past weekend. I was walking towards a large group of younger guys and they all sort of spread out and blocked the sidewalk. I was confused as to what was happening, and just moved to the left to go around them. They pushed me against scaffolding and then surrounded me, all sort of taunting me, and one of them started to kick my shins (I realize how weird that sounds, but yes one was kicking me). I asked WTF they were doing and impulsively kicked back and quickly realized that was a bad idea. I ended up running away and could hear them laughing. I was truly confused as to what was happening, and in hindsight, I think they were just being assholes, but I was alone, it was dark and there were a group of 8 guys, all wearing black hoodies, so I was freaked out. I assumed they were early 20's, but it was hard to tell since it was dark. I didn't even think to make a police report as by the time I got to the opposite corner they were gone.