Los Angeles city and school police were investigating a large fight Wednesday at Crenshaw High School involving 50 to 100 students, officials said.In an unrelated incident at the East L.A. Skills Center, a school police officer arrested an adult student who was allegedly in possession on campus of a loaded 9-millimeter “ghost gun.”The Crenshaw fight was reported around 9:30 a.m. at the high school, at 5010 11th Ave. in the Hyde Park neighborhood of South Los Angeles. LAPD officers responded, and Los Angeles School police dispatched 10 officers.A school police spokesman confirmed the fight involved perhaps 100 or more students as either participants or onlookers. Crenshaw High’s enrollment is about 500 students.Early reports are that there were no significant injuries or arrests, and LAPD officials said no firearms were used. School police are still collecting information at the scene.Gil Gamez, president of the Los Angeles School Police Assn., said the Crenshaw incident apparently arose out of a fight between two girls last week. “The girls recruited family and friends over the weekend,” Gamez said. “Family and friends showed up today.”The fight began in front of the school but spilled onto campus in the quad area, he said.School police spokesman Sgt. Rudy Perez could not immediately confirm those details but noted that there was an incident Monday in which two adults went onto campus and tried to fight with a student.In the wake of the disturbance, the school was placed on lockdown, and officers were to be stationed there for the remainder of the day. In years past, one school police officer would be stationed at each high school. However, school police are no longer allowed on campus — after a decision by the L.A. Board of Education in response to student activists. Patrol officers are on call when incidents arise.Reductions in the school police force make it more likely that Los Angeles city police also will be called when there is a larger disturbance or a more serious incident. It is not unusual for both police agencies to be summoned in a situation that could involve crowd control or a detailed investigation.At the East L.A. Skills Center in Lincoln Heights, a school police officer was on campus to investigate a small-scale fight Wednesday morning when an administrator and a student approached her, Perez said.The two were concerned about an unrelated situation — a student who had previously talked about bringing a gun to campus and who appeared to be acting erratically that morning.The officer directed the student in question, a 22-year-old, to step out, and found in his possession a fully loaded, 9-millimeter Glock ghost gun.A ghost gun is a privately made firearm that lacks commercial serial numbers that are frequently used to trace a weapon.The student with the firearm was taken into custody, Perez said.