Causes for stage-rage:
Bad soundchecks - Balance is important. Poor balance between sounds can turn a good performance bad. Perhaps a guitar isn't turned up the whole way. Other times the drums drown out the singer. It's important that the sound guy balances and mixes all the channels correctly.
"Forget this. I can't even hear myself."
Reduced time slot - Sometimes, owners pull the plug on an act that's tanking quickly. Other times, an artist goes beyond its allotted time. Either way, nobody wants his/her time cut short.
"You're going to give me ONE FUCKING MINUTE? You've gotta be fucking kidding me."
Poor security - Security is responsible not only for making sure everyone in the crowd is behaving themselves, but that the artists are safe as well. Rewind to 2004. Security failed to catch a deranged fan before he jumped onstage and murdered Pantera guitarist "Dimebag" Darrell Abbot. Artists even take matters into their own hands in spite of bad security. A few years ago, Randy Blythe of Lamb of God was accused of manslaughter when he pushed a fan off stage. Security failed to stop the fan the previous two times he jumped onstage.
"Thanks to the lame-ass security, I'm going home."
Cantankerous crowd - The paying public knows what it wants. They can quickly turn on an act that's boring, combative or performs poorly.
"Up to you. Do you want to hear some rock 'n roll or do you wanna go home? See ya."