You have to find some humorin this Washington Post report on a political rally turned violent.
The video makes it hard to see what sparked individual violent incidents. At one point, two men began punching each other. A woman was hit in the face in the scuffle, further angering people. As that was going on, someone released a mist of pepper spray, and people in the dense crowd started coughing and rubbing their eyes.
Then, the mood of the rally soured, according to the video.
Yes, only then did the mood sour. Until then it was going swimmingly.