The US site runs under some really tight restrictions, you can only use it on a mobile phone where your network provider verifies your location is in Nevada (and Delaware maybe?), and you can only deposit cash into your account via a few physical locations.

I'm pretty sure William Hill operates legally in Nevada. They operate many of the sports books at smaller casinos there and I think offer betting shops outside of casinos there as well, like in sports bars. Nevada also allows online sports betting.