This isn't a specific response about what the OP alleges to have seen after the game, but in response to questioning about the school. Maybe I can help reduce some ignorance. I didn't go to that school, but grew up and live in the area.
El Cajon Valley HS is in the center of the City of El Cajon, in San Diego's East County. It is in the Grossmont League, if that matters. The school district has a broad spectrum of demographics, ranging from densely urban to very rural, with family incomes ranging across the board. The school itself is in an area that has had a dramatic change in demographics over the last 20 years. I suppose the school's immediately surrounding community would be referred to as "low income". There is a lot of high density housing. It has seen a large influx of refugees and immigrants from areas of conflict. Many of the kids that go to that school are happy just to be able to attend school and play a sport without worrying about being killed. Their life experience is far different than my daughter's, or probably almost anyone else's that is on this forum. There is no excuse for what was alleged to have happened, but I thought it might help to know who is being talked about.
There is a soccer club (Yalla) based at the Boys and Girls club about 1/4 mile from the HS. I'm sure that many of their players go to El Cajon Valley HS. Yalla has a mission to provide soccer opportunities to the immigrant/refugee youth in the community. I refereed a BU16 game of theirs. Aside from normal teenage boys stuff that you get from all games in that group, the Yalla team was the most respectful to me that I have encountered at that age. These kids get very little parental support from what little I have seen of their games. I suspect that what parent's they do have here are working hard just trying to get by in a strange land.