You'd never be prosecuted for watching a live broadcast hosted by the actual content provider (say, a US TV station). The responsibility to show their content only to US customers is entirely on their shoulders; without the restrictions they put in place, anyone would be able to view it since it's on the Internet, which will never obey country boundaries no matter how hard people try to make it do. If you can get past their measures (which you might not be able to, if they're doing their jobs properly), go ahead.