The clearest example
In February 2016, during his campaign for president, Trump told a crowd in Cedar Rapids, Iowa, "So I got a little notice. We have wonderful security guys. It said, ‘Mr. Trump, there may be somebody with tomatoes in the audience.’ So if you see somebody getting ready to throw a tomato, knock the crap out of them, would you? Seriously. Just knock the hell .... I promise you, I will pay for the legal fees. I promise. I promise."
As a review of the video shows, Trump is not smiling or chuckling as if this was intended as a joke.
Other examples of Trump speaking favorably of violence
On several other occasions, Trump invoked violence without necessarily inciting it. (Hat tips to the Washington Post’s Aaron Blake and Mashable for collecting a number of these in one place.)
• August 2015. At a press conference in Michigan, Trump contrasted his interactions with the public with those of Democratic candidate Bernie Sanders, who had recently faced opposition from Black Lives Matter protesters.
"That will never happen with me," said Trump, according to a dispatch by the Washington Post’s David Weigel. "I don't know if I'll do the fighting myself, or if other people will. It was a disgrace. I felt badly for him, but it showed that he was weak. You know what? He's getting the biggest crowds, and we're getting the biggest crowds. We're the ones getting the crowds. But that's never going to happen to Trump."
• November 2015. At a rally in Alabama, Trump said about a protester, "Get him the hell out of here, will you, please? Get him out of here. Throw him out!"
The following day, calling into Fox News, Trump responded to a question about allegations that the protester had been "roughed up." The protester, Trump said, had been "so obnoxious and so loud ... maybe he should have been roughed up. Maybe he should have been roughed up. Because it was totally disgusting what he was doing."
• February 2016. At a rally in Las Vegas, Trump again responded to a protester:
"See, he’s smiling. See, he’s having a good time. Oh, I love the old days, you know? You know what I hate? There's a guy, totally disruptive, throwing punches. We're not allowed to punch back anymore. I love the old days, you know what they used to do to guys like that when they were in a place like this? They'd be carried out in a stretcher, folks. Oh, it's true. … The guards are very gentle with him. He’s walking out with big high-fives, smiling, laughing. I’d like to punch him in the face, I’ll tell you,"
• March 2016. At one point at a rally in Michigan, Trump reiterated his pledge to pay legal fees for people who remove protesters. "Get him out," Trump said. "Try not to hurt him. If you do, I'll defend you in court, don't worry about it." (Trump later said he had never made the pledge to pay legal fees.)
• March 2016. At an event in Palm Beach, Fla., Trump referred to a past incident with protesters. "We have had a couple that were really violent, and the particular one when I said I'd like to bang him, that was a very — he was a guy who was swinging, very loud and then started swinging at the audience and the audience swung back, and I thought it was very, very appropriate. He was swinging, he was hitting people, and the audience hit back, and that’s what we need a little bit more of."
• March 2016. At a rally in North Carolina, Trump said, "In the good old days this doesn't happen because they used to treat them very, very rough. And when they protested once, they would not do it again so easily. But today they walk in and they put their hand up and they put the wrong finger in the air at everybody. And they get away with murder, because we’ve become weak."
• March 2016. At a rally in St. Louis, Trump once again addressed protesters who were being removed from the facility.
"Part of the problem and part of the reason it takes so long (to remove the protesters) is nobody wants to hurt each other anymore, right? And they're being politically correct the way they take them out. So it takes a little bit longer. And honestly, protesters they realize it -- they realize there are no consequences to protesting anymore. There used to be consequences. There are none anymore."
• March 2016. At a rally in Kansas City, talking about someone who had rushed the stage, Trump said, "I don't know if I would have done well, but I would have been out there fighting, folks. I don't know if I'd have done well, but I would've been — boom, boom, boom. I'll beat the crap out of you."