A woman wearing a Donald TrumpDonald John TrumpRussia's election interference is a problem for the GOP Pence to pitch trade deal during trip to Michigan: report Iran oil minister: US made 'bad mistake' in ending sanctions waivers 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 ClintonTrump rips Krugman, NYT after columnist writes GOP no longer believes in American values Klobuchar jokes to Cuomo: 'I feel you creeping over my shoulder' but 'not in a Trumpian manner' Dems seek to rein in calls for impeachment 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.

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.