In Brattleboro, Vermont, a bunch of people decided to take action against a move they said was damaging to the environment. In their peaceful protest, they refused orders from the police to disperse. Further, they shackled themselves in such a way that they could be free whenever they wanted, but the police would need special tools (such as a jackhammer) to get to the locks.
The police didn’t have jackhammers, so they used a tool that they did have at hand.
It’s a simple principle: one does what the police tell you to do, or they use force. In this case, the police had tasers on hand, and they used them to get the people to obey the police’s lawful orders.
In other cases, the police have used pepper sprays and other less-than-lethal methods.