When two girls started brawling at Chase Middle School last week, several other students responded as kids tend to do nowadays: They pulled out their cellphones and started recording. But the school district has a rule against filming fights, intended to stop such videos from ending up on YouTube or circulating on Snapchat. “If you’re videotaping a fight, that’s encouraging fighting,” said Mark Sterk, the district’s safety and security director. “And we don’t tolerate that. We don’t allow that.”