Don't stand right behind and attempt to obstruct a car that's trying to back up. Play stupid games, win stupid prizes.
(I say this despite mostly supporting the political cause that the students are championing. I wish they were smarter and more disciplined, so that they would win more battles.)
In NY, motor vehicle operators have the responsibility to not run over pedestrians. It doesn’t matter if they’re standing behind you or obstructing you. No one has the right to strike someone with their vehicle. The video is clear that the president was negligent in operation of the vehicle.
I’m not sure why this is hard for you to understand, but I hope you don’t operate motor vehicles if you can’t grasp this.