I don't know about the rest of the story but from the actual video:
-Cobain didn't jump off his back, he just jumped into the crowd
-The guy didn't pull him back on stage. Cobain was floating on the crowd toward the stage and the bouncer has his hand pushing Cobain's face to keep him in the crowd
-Cobain then smashed the butt of his guitar twice into the head of the bouncer
-Cobain got on stage and started to get to his feet and then the bouncer punched him in the back of the head
-The bouncer's face was covered in his own blood
Crazy, but that is what the video shows. I am not sure about why the bouncer was so pissed at Cobain but I read that the band had been using his PA and it was working poorly and Kurt had been smashing it with his guitar out of frustration and hence the pushing of his face when he went into the crowd.