Trump still seems awfully confused, especially for someone running for POTUS, about the first amendment. After announcing that he wants to restrict the press, he's now saying that his free speech rights were violated when he canceled a rally on Friday night.
The first amendment protects you from having your speech restricted by the government, not from people protesting against it. Trump's free speech was never in peril since the government didn't shut down the rally, nor was it aiding the protesters in doing so. In fact, if the police had removed all of the protesters from that public space (and an arena in a public university certainly is a public space) in order to allow the rally to go on, the protesters' constitutionally-protected free speech rights would have been violated which is not acceptable.
However, there are other concerns here. No one should use violence or its threat to stop people from speaking. Ever. Not the protesters, not Trump. I will never, ever be proud of violent protests. No matter what Trump has said, no one should be violent toward him or his supporters and no matter what the protesters say, no one should be violent toward them.
Unfortunately, Trump has been documented a number of times espousing violence to shut down protesters. Not only has he encouraged violence against protesters, he has offered to pay legal fees for his supporters if they are arrested for being violent (including, apparently, a man who punched a protester with no visible provocation and who later threatened more violence against the protester). His speaking out against violence directed towards his own supporters is not enough.
Trump has the right to stand up and say what he wants to without government inference. He has taken full advantage of that and is effectively using hate, fear, anger, greed, and pride to stir people up. However, constitutionally-protected free speech doesn't also come with freedom from protest and disagreement, even noisy and disruptive disagreement. If hate- and fear-inducing speech comes back to inconvenience him (and the canceled rally was an inconvenience, not a violation of free speech), then that's a consequence of the words he chooses to use.
Trump has made it clear that he doesn't think he's the problem and I don't think that will change. Mostly, I just want no one to get seriously hurt.