I can totally understand banning Wifi hotspot access points at big crowded events like this. Just a few dozen in the same area is enough to completely use all available bandwidth in the form of beacons. Performance will suck for EVERYONE, including the venue WiFi.
Why not just use a cable? Most phones support tethering over USB, and it'll even perform better than WiFi hotspot mode because it's a direct cable connection so the only RF you're doing is cellular. I always try to do USB tethering when possible to avoid polluting the airwaves with my needless access point.