Authorities are investigating a fight that broke out during a mini Olympics event at the Santa Rosa High School stadium.
Santa Rosa police reported that all classes competing against each other on different activities.
But investigators said that two classes charged each other during a large-scale disturbance around 10;30 a.m. Friday.
Police said one teenage boy exposed his rear while another made an obscene gesture with his middle finger.
During the brawl, a female allegedly assaulted an officer by slapping his forearm as he was trying to escort a student from the stand.
Officers arrested three students. The two boys were charged for disorderly conduct while the girl was charged for assault.
Officers escorted another five students off campus where their parents were called to pick them up.
School officials cancelled the rest of the games.
Santa Rosa police are still investigating the incident and reviewing cell phone video taken at the scene.