Another night on Haight St with the SFPD

I went to a friend's art show opening yesterday on Haight St. As we were leaving, we noticed that there were a group of police officers in the middle of the street we had to cross to get back to where I parked my car. So instead of walking straight, we turned up the street, and stopped in front of a way cool furniture store to survey the scene. At this point there were people milling about (this is a Saturday night around 8ish), taking pictures of the cops. My friend and I looked up the street and there were about 20 police officers in full riot gear walking single file down the street, headed straight for the middle of the intersection on Haight st. And this is not the busier The Haight, this is just a random neighborhood, with not even that many shops or businesses. The oddest thing is not a single person had a clue as to why the cops were there. According to one guy there "maybe was a protest (earlier) that afternoon - maybe". I searched the newspaper this morning- not a single mention. I am still baffled as to why I had to dodge amored police vehicles and motorcycle cops on the way to my car (and then out of the area) last night.