Great performance. Thanks OP for posting.
As I recall, Tony Iommi was sick that day. And Barry Williams (a superstar at the time, Greg Brady from the Brady Bunch) offered to play guitar for Black Sabbath. Ozzy gratefully accepted, and the rest is history.
But as you know, all that's just BS.
This is one concert where you can see Tony goofing off with Ozzy (11:10), which he normally seldom if ever did because he was too focused on playing. Great concert, great fun, great rockin.