It was "activism" because he was filming this and had every intention of turning it into a public matter. I think it's just a poor form of activism. Sure, the cop may have gone a little overboard, but it's hard to verify from the video what exactly happened, especially after Derrick fell off his bike. Even so, Derrick was obviously acting like an idiot. I'm sympathetic to the liberty activist folks in Keene, but when someone who is sympathetic toward your cause is questioning the wisdom of your activism (or activities), I think it's a pretty sure bet that those who are indifferent or hostile to your cause will definitely not be supportive or swayed.