They're lucky they didn't get summarily shot in the eye sockets with "non lethal" pepper balls. BPD was a bunch of unaccountable thugs, and this "incident" was yet another for the highlight reel. When the Sox finally won the Series and we were all out celebrating on Comm Ave only to be attacked by those juiced-up-on-federal-terrorism-propaganda paramilitary fuckers, I was hoping I was going to get to bat one of their grenades back at them with the broom I was carrying (sweep!).
What you experienced is unfortunately the system working as intended. Putting the jackboot on the throat of anyone who gets ever so slightly of line (like some rowdy sports fans) is exactly what the people of MA want their bored and over-funded cops doing.
I lived in Boston through much of the 80's, the BPD has always been jackbooted thugs. We looked into it. The phrase originated at the start of the 80's and the BPD embraced it like their identity.