What do you do?
You stop them first, ask questions later.
Whether you are a paid pro or a volunteer--or just an amatuer who got involved, failure to do so could cost the life of the principal.
In retrospect, this was a set-up, and the guy with his foot on her head was a plant.
That the persons who stopper this person only grabbed her and wrestled her down (end of the play act), is to their credit.
I have read/heard/seen nothing to indicate this person sustained any serious injury. Remarkable restraint, not brutality.
She just as easily have had a gun, grenade, or other weapon or destructive device and malicious intent.
An employee of Paul, that has issued an apology, is a MoveOn plant?
Did you notice she was stopped, and laying in the gutter being held down, when the foot came in? Any possible danger was over. Does that clear fact matter?