http://archive.scripting.com/2004/01/23#theFamousDeanRant
I asked Jim Moore what that was about, he said it’s an Indian war yell or something like that, they used to do it in United Farm Workers rallies, and they adopted it at Dean For America. A few minutes later Dean let out the famous scream, it was the same scream I heard in the conference room.
They’re probably not saying this publicly because it wouldn’t seem contrite to do it, and they probably know they’d get roasted for saying the scream and ranting you heard was part of the motivational culture at DFA. Some have compared the Dean speech to a similar rant by Microsoft CEO Steve Ballmer that made the rounds of the Net. So Dean gets a bit whacky, but after seeing it so many times, the shock value is fading. Taken at face value it wasn’t anger, it was a steam-letting, and an attempt to rally the troops, and totally understandable. The press, as usual, is making a big deal of catching a candidate being a human being.