You are well within your rights to record cops while they're on the job in MA. A guy got a 6-figure settlement a few years back after the cops took his phone or some shit after he was recording them. More recently there have been a couple cases of cops in Boston trying to intimidate people out of recording them or once again taking their phones but once those stories hit the news it's reiterated that you have a right to film cops while they're on duty. Then again these guys are mostly scumbags, I saw one video in Boston where the cop straight up lied to the guy recording him saying "I didn't give you my permission to record me" when I'm sure he knows damn well it wasn't needed in the first place..