I had a similar issue. I was using the BBC sports app on my phone (as opposed to the BBC sports web pages) but when the live match feed was on there wasn't a button at the top right of the video to start the cast. And I launched it a couple of times just to make sure.
There was a cast button on the top bar of the app that was visible if I hadn't selected the full screen video option. When I selected that, the phone/app did connect to the Chromecast, but just displayed the message "waiting for media stream".
Without doing a POR of either phone or Chromecast, I ran the Now TV app instead and was able to cast the match stream from that.
Don't think it was a hardware issue.