[alexlmiller]

Two problems with that approach at large scale shows:

1) These days the cabling is run inside a run of barricade bisecting the crowd, so it's in a secure area the entire time

2) Modern PA systems at shows of that size have almost exclusively moved to digital snakes / audio networks, not analog

To realistically pull that off you'd need production access to the event to tap into the audio network and re-route things. That said, given the number of people with appropriate access and the fact that InfoSec isn't a high priority, that actually seems pretty doable.

Once they realized what was going on though, a few breakers flipped would drop power to the amps or speakers (depending on whether using powered or passive arrays) and it would be over (which would happen pretty quickly since the power distro is very well organized and labeled since quick troubleshooting is often necessary).