You have the entire story wrong. The "heckler" was another person on the open mic. He was told he would get more time and the other guy pulled him at 6 minutes. Hence the opening where they are both at the mic and he says "you fucking lied to me."
The other guy has the right to pull him early. That kind of stuff happens from time to time, and is usually not a big deal. The guy who was being pulled seems like he had his hand on the other guy's shoulder or something similar. The host freaked out at this and is screaming "don't touch me".
The guy went back to his seat and obviously most of the limited audience was on his side. He was seated again and the host (despite everyone saying move on) just kept insulting him til the guy got up and approached while saying "are you trying to start shit with me?" This clearly could have been deescalated, but the host was trying to start shit.
Someone touching you in an obviously non violent way does not give you leave to dropkick them in the stomach. If the guy had been pushing the host or something it would be a much clearer motivation.
In this instance the host either should have told him to go outside or moved on. Instead he did painfully unfunny insults and literal schoolyard bullying until the guy re-engaged and even then gave no actual sign that he was going to be violent.
Why are you fighting so hard to defend an obvious bully who the rest of the audience (who are experiencing this real time and not an edited video) are clearly not on his side?