News reports called the person whose arm was injured an activist, a perfectly good word for what she was on that day. Around the same time, an article by Astra Taylor in _The Baffler_ informed people that "Activists are types who, by some quirk of personality, enjoy long meetings, shouting slogans, and spending a night or two in jail" and "Activists seem to relish their marginalization, interpreting their small numbers as evidence of their specialness."
When Trump started to win in the primaries, some people brought up violence against anti-Trump protestors at his rallies as unprecedented, as something that signaled a kind of proto-fascism that hadn't been seen in recent America. And they didn't want to hear about the end of Occupy, about the people arrested for wearing the wrong T-shirt at George W Bush rallies, about how almost every protest in America that ever made a difference has involved violence by security forces. That was official violence and, I guess, not as scary to some people as unofficial violence, even though official violence usually additionally results in the victim being arrested and charged.
People in America, in general, reflexively dislike protest and support authority. That's as true for most of the putative left as it is for the right. Liberals are already starting to denounce the anti-Trump protests as violent or just ill-mannered, old-style leftists are eager to denounce protest movements for "individualism", and the right is, of course, bringing out old standards about professional protestors.
The people injured in the #NoDAPL protests are not being injured by fascist brownshirts: they are being injured by traditional American use of state and local security forces. Those forces are just as unimpeded by Obama as they would be by Trump. Maybe Trump will be even worse. But what's happening at the DAPL protests is fully in keeping with American history, especially the history of what happens to native people when their land has some kind of resource.
Protest strategy in the Trump era is going to be difficult to work out. The people newly encouraging protests are the worst kind of fair weather friends: when someone like Jonathan Chait writes "The day after the election, protesters swarmed the streets of major cities shouting that Trump was 'not my president.' Good for them." you know that this good-for-them is going to last about a month before Chait gets alarmed and returns to form.
I'm not encouraged by the recent, brief upsurge in support for protest against Trump. It's not being generalized to cases like the DAPL protests where shocking abuses by security forces are ongoing, because that would involve condemning the system as a whole instead of just half of it. People are too eager to return the system to a nonexistent age in which stability and safety meant that protests really were bad for everybody.