Yeah... no. 'Free', 'sport' and 'HD' don't go together well in a sentence. With enough digging you can find watchable streams of anything from F1 to the Russian badminton championships, but anything claiming to be HD likely isn't.
Best option is to get someones premium DSTV account and login to the website here http://www.supersport.com/. Need their smart card number and ID number.
The Supersport app sucks a bit so you only get HD half the time no matter how good your Internet is.