I haven't used a MVNO at a packed stadium, but I've never experienced complete bandwidth starvation even in large crowds. I've also never had any problems with

I haven't used a MVNO at a packed stadium, but I've never experienced complete bandwidth starvation even in large crowds. I've also never had any problems with tethering on a MVNO; I think the restrictions are only for the "unlimited" plans which don't make a lot of sense (may as well get service from the major carrier at that point). In my experience, if you're paying for x GB per month, you are free to use that via tethering without extra interference from the carrier.