It should be noted these are State Troopers, who basically follow Abbott's orders these days, and are always itching to put on a show for the cameras, eg the one above. APD and UTPD don't seem to be involved in this.
Edit: UTPD was involved:
UT Police Assistant Chief Ashley Griffin issues a dispersal order to those present. That statement was read over campus loudspeakers, Ryan Chandler reports.
“I command you in the name of the People of the State of Texas to disperse, and if you do not, you shall be arrested for Violation of Penal Code Section 42.01 Disorderly Conduct, 42.02 Riot, 42.03 Obstructing a Highway or other passageway,” the order reads.
From everything I've seen, this was a peaceful, mobile protest that caused no disruptions until the police caused disruptions.