Why did Ozzy walk off stage in Dallas 8/24/1975

I attended a Black Sabbath concert in Dallas Texas on August 24th 1975. The tour was for the "Sabotage" album. It took place at Memorial Auditorium(now called the Dallas Convention Center). Brownsville Station was the backup band. During the show Ozzy walked off the stage in the middle

 of "snowblind". This was the 3rd or 4th song of their set. The band continued playing for a few more notes and then stopped and walked off stage too. The house lights came on and after about 15 to 20 minutes Ozzy came back onstage and started a speech about how rock and roll is free, and let my people go(WTF??). The band then started the song over and completed the concert. Great concert, but I still have not been able to find out what caused the walk off. If anyone knows the answer add a comment to this blog. The next morning I had to attend the first day of school for my senior year at Arlington HS. That was a rough day.