Here you go assuming interruption of service is synonymous with jamming. Since many BART stations are underground, interrupting service is as simple as powering down repeaters. Nothing illegal about that, BART owns the repeaters and operates them under license from the service provider(s) and can do whatever they want with them including removing them altogether. Service underground is a courtesy to the riders, nobody ever said anyone has to be courteous to hooligans.

"But why just a station?"
Because that's where the repeaters are.