Here is a video of the recent Seattle protest from an aerial view. There’s no escaping this. https://www.reddit.com/r/Seattle/comments/gv0ru3/this_is_the...
You say this like it's a conspiracy when there are clear maligned motives for cops to approach these things in this manner, as well as a history of it.
Sometimes, but not often.
More often, when there is a gross “overreaction”, it's a calculated attempt to suppress the message of the protestors, coordinated by leadership and instigated by various means including feeding false intelligence to the cops on the line that distorts their interpretation of facts.
But in the case of race-related issues it's often much worse than that, and this is apparently the case now. The infiltration of American law enforcement agencies by white supremacists is long-documented, there is, at the moment, an active white supremacist effort to trigger a race war, and the President of the United States is actively using language invoking historical racist government violence, and directly initiating violence against peaceful protestors. This isn't impulsive police violence, or merely violence as instrumental to winning a political debate, this is a (mostly loosely) coordinated campaign of racist violence where the violence and the harms it inflicts is, itself, a goal, and not just a callously accepted cost of some other end.
[1] https://www.reddit.com/r/ThatsInsane/comments/gv2ogk/news_ch...
This is typically after police have antagonized the situation and created it through tactics like kettling and surrounding protesters and then throwing grenades of tear gas and misusing rubber bullets in potentially lethal ways on nonviolent crowds.
"declared a riot" is political speak for when the police don't like a protest and begin attacking.