There has been some discussion that the videos posted so far are heavily edited to make the police look as bad as possible and him to look as if he is being manhandled for simply asking a question.
This discussion came up on fark.com and with the number of people who read that site you can usually count on someone posting who has first hand experience (case in point, during the VT shootings there was a running thread with real time information being posted by the students on that campus).
Anyway, from what some people said who claimed to be there, the timeframe for student questions had expired and the guy who got tasered basically wasn't going to leave unless he got to ask his question. He forced his way past several other people who had been waiting in line and grabbed the microphone and demanded that Kerry take his question. That is why in the video the police are standing behind him already when he is asking his question. They had already moved into place to remove him when Kerry indicated that he would answer his questions and told him to wait until he finished answering the question he was already on. When he began to ask his question it basically turned into a diatribe, and after approximately a minute of him demagogueing the university cut the audio to his microphone. This didn't stop him, and when the police moved forward to remove him from the building, he began yelling at the police and pulling away from them. At that point, the police tried to take him down and somewhere in the process he got tased.
The only question I have is did he get tased after the handcuffs were on him as some people are claiming? If he was tased so that he could be cuffed, well he pretty much deserved it.