I watched this video with incredulity:
It matters not one whit whether the students hold disagreeable opinions. No one of common sense can watch that video and say, "That's just how the cops should have handled that."
More to the point, unless you feel like tossing "rule of law" into the toilet, and I presume we're not there yet, the courts have ruled under relevantly similar circumstances that this constitutes excessive force--and the police should have known that. This was thoroughly hashed out in Headwaters Forest Defense v. County of Humboldt:
In addition, regional and state-wide police practice and protocol clearly suggest that using pepper spray against nonviolent protestors is excessive. The law regarding a police officer's use of force against a passive individual was sufficiently clear at the time of the events at issue in this case that the defendants cannot claim qualified immunity on the ground that they made a reasonable mistake of law. See Saucier, 121 S.Ct. at 2158.
If they didn't know it, they failed Policing 101. From the archives of The Police Chief: Chief's Counsel: Police Use of Force: The Problem of Passive Resistance:
In conclusion, passive resistance strategies can create difficulties for law enforcement officials attempting to intervene in protests and demonstrations. Usually the severity of the crime being committed is minimal; nonviolent protestors generally pose no immediate threat to the safety of the officers or others; the protestors do not actively resist arrest; and the protestors invite arrest, rather than attempting to evade arrest by flight. For these reasons, when confronting passive resistance strategies during protests and demonstrations, law enforcement officials must carefully select use-of-force tactics and properly control their application.
You know what else common sense says? If the students want to camp in the quad, let them. UC Davis Police Chief objected to it on the grounds that it wasn't safe. This doesn't look like an improvement, does it? So they camp in the quad. If I were a parent, "camping in the quad" would be the least of my worries about dumb, dangerous things my kid might do.