When using Safari on iPhone, it is usally the website that decides whether to push a mobile version of a site. When a web developer such as the ones who wrote the website for ESPN, they have the ability to tell which browser you are using when you access the site.
So, that being said, there is no way to force safari to pull the normal page, that would be up to the developer of the webpage. That being said, I took a trip on over to the ESPN webpage on my iPhone. It looks like if you scroll all the way to the bottom you can click on the ESPN.com link and it will take you away from the mobile page, and give you the full content page you would normally see on your computer.