A woman wearing a Donald TrumpDonald John TrumpWhere do we go from here? Conservation can show the way Gov. Ron DeSantis more popular in Florida than Trump Sotomayor accuses Supreme Court of bias in favor of Trump administration MORE for president jersey was cornered by dozens of protesters on Thursday and pelted with water bottles and eggs.

It was one of several incidents of violence at a rally for the presumptive GOP nominee in San Jose, Calif., the most disturbing scenes yet of increasingly frequent confrontations on the 2016 campaign trail.

NBC News reported that several Trump supporters were punched or chased as they left the event. Video showed protesters taking a red Trump hat from one man and setting it on fire.

San Jose Police Sgt. Enrique Garcia told NBC News that several protesters were arrested and one officer was assaulted in the melee, NBC reported.

John Podesta, Hillary ClintonHillary Diane Rodham ClintonRussian interference reports rock Capitol Hill Judge dismisses Nunes' lawsuit against Fusion GPS The Hill's Campaign Report: What to watch for in Nevada MORE’s campaign manager, condemned the violence on Twitter.

Political commentator Mark Halperin of Bloomberg criticized police, questioning why they didn’t step in earlier. 

Law enforcement in the city "really dropped the ball," Halperin said.

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The incidents are likely to raise pressure on police in Cleveland, where the GOP is hosting its national convention this summer, to take additional steps for ready for big protests planned against Trump.