— -- Donald Trump's rally in San Jose, California, Thursday night was marred by violence by anti-Trump demonstrators who targeted the event's attendees and police.
San Diego police reported that approximately 300 to 400 protesters gathered outside of Trump's event, which led to four arrests for "for incidents including assault with a deadly weapon and unlawful assembly," Officer Albert Morales said in a statement.
"While several physical assaults did occur, the police personnel on scene had the difficult task of weighing the need to immediately apprehend the suspect(s) against the possibility that police action involving the use of physical force under the circumstances would further insight the crowd and produce more violent behavior," Morales said.
A police sergeant was one of the ones who dealt some of the brunt of the violence, suffering minor injuries "after a protester struck him with a metal object."
Trump's foes surrounded the San Jose Convention Center, where scuffles broke out between them and Trump supporters. Some of the altercations were physical, resulting in bloody injuries, as in the video below.
Some Trump protesters surrounded the car of a presumed Trump supporter as the vehicle was leaving the convention center's garage. Protesters were shaking the car and smashed its taillight. Protesters also surrounded and banged on police cars.
Rally attendees heading back to their cars were egged, followed and intimidated by some of the protesters. At one point, a large group of demonstrators surrounded a Trump supporter, throwing bottles and spitting at him as he walked back to his vehicle.
ABC News' Tom Llamas and Alex Stone contributed to this report.