1) they were crouched and linked together, not moving after repeatted warnings to move away.
2) even after pepper-sprayed, they held their line and neither mover nor cooperated with arresting officers.
3) while it appears excessive without the full context of what preceded it explained, it was not excessive force, according to several police-procedure and legal experts I saw discuss it. It looks from the video like the cop just walked up out of the blue and sprayed them without warning. In truth there were repeated warnings, and even after being pepper-sprayed, they wouldn't budge without some minor degree of physical action by police.