A couple of people have reported this in the past.
If i remember correctly, somebody over on Twitter found a workaround by temporary enabling subtitles and then disabling them again.
I can't remember if it was done under the NOW App when watching something via the bubble speech icon or in the Android Closed Captions settings itself.
This is a bug I've come across as well but it's usually quite easy to solve though. It can occur on all linear channels though not just Sports. When on the linear channel of your choice tap the screen to bring up the playback controls. Then tap the speech bubble button on on the top right this should bring up the language selection options for subtitles and audio in the audio options tap English. That should solve your issue
It would appear the app sometimes the app fails to properly select an audio track when you start a linear channel stream. A bit odd I know.
@commanda6 that doesn't work for me and I only have the problem on live sports. I have to exit the stream and enter again. Sometimes it takes 4, 5 or 6 attempts to get audio going.
@Simon-J can this be looked into as there are more and more threads appearing complaining of the same. I first noted this issue in May.
@Saint1976 . It's interesting to note that when you first noticed this in May, that this is around the time when the android app for android tablets was last updated according to the Google play store