If you pay for cable, you probably pay for ESPN. Disney's sports empire is practically inescapable, especially if you watch college sports, and it's essentially impossible to pay for conventional television without getting ESPN thrown into the package, whether you want it or not. So if you're paying for it, you might as well get it on your phone too, right? ESPN's live streaming service WatchESPN is now available within the primary ESPN app itself. Previously WatchESPN was a separate Android app.
To access WatchESPN, open the standard app, log in with your ESPN account (don't bother using the Facebook integration because you still have to have a separate ESPN account for some God-awful reason), then tap the TV icon in the upper right corner. Before you tap on any of the live or pre-recorded content, you'll have to sign in with your cable or satellite provider account. At the moment it looks like ESPN's system works across pretty much every notable cable company in the US... which is about right, since every single one of them forces you to pay for ESPN. (I'm not bitter, really.)
ESPN's app doesn't work with Android TV, but then, before today it was mainly for sports scores and web news. And anyone likely to actually watch ESPN content on a television probably already has some kind of set-top box set up. Chromecasting of the videos themselves is not supported, but the ESPN app doesn't use the API block to black out the video if you cast the entire phone screen (like the NFL Mobile app does). It's not clear if the separate WatchESPN app will be maintained.