Multiple videos, including CNN's footage, show campaign manager Corey Lewandowski reaching for the man's collar as a member of Trump's security detail also grabs him from behind.
"Corey Lewandowski was speaking with a protester at today's rally in Tucson, Arizona when the individual he was speaking with was pulled from behind by the man to Lewandowski's left," Trump campaign spokeswoman Hope Hicks said in response to a CNN inquiry, referring to a member of Trump's private security detail.
"The video clearly shows the protester reacting to the man who pulled him, not to Mr. Lewandowski," Hicks said, adding that Trump "does not condone violence at his rallies, which are private events paid for by the campaign."
Lewandowski and the young man appear to exchange words in the moments before the altercation. Hicks said Lewandowski "simply asked the protester to leave."
"Instead of exiting, the protester grabbed the woman in front of him (in the green shirt), which is when the man to Corey's left and many others in the scene react to her wincing," Hicks said.
The protester had been asked to leave once prior to the altercation, according to two sources familiar with the incident. He was able to gain entry back inside before Lewandowski and security removed him for a second time, the sources said.
Trump on Sunday called Lewandowski's involvement in ejecting protesters "spirited."
"Security at the arena, the police were a little bit lax. And he had signs -- they had signs up in that area that were horrendous, that I cannot say what they said on the sign," Trump said on ABC's "This Week." "I give (Lewandowski) credit for having spirit. He wanted them to take down those horrible profanity-laced signs."
Republican National Committee Chairman Reince Priebus said Sunday campaign officials should avoid "getting involved in confrontations."
"Getting involved is not the answer. I think you leave these things up to the professionals. You've got professional police; you've got Secret Service," Priebus told CNN's Dana Bash on "State of the Union."
"It's certainly not something that we would condone as far as the continuation of violence -- and it goes to both sides," he said. "It starts with agitators, and then people take matters into their own hands. It just obviously doesn't work."
The incident comes after reporter Michelle Fields this month accused Lewandowski of grabbing her by the arm and yanking her backward as she tried to question Trump at a news conference. Lewandowski has denied that he touched her. Fields has pressed charges
A short time before the encounter with Lewandowski, a man attending Trump's rally appears to have sucker-punched a protester as the protester was being escorted out by security, according to multiple videos, including footage from CNN.
The man punched and kicked the protester before police officers rushed to the scene to detain him, the videos show. Sgt. Kimberly Bay with the Tucson Police Department said in an email that Tony Pettway, 32, was arrested for misdemeanor assault and released.
Trump's response to that incident was that protesters "are not innocent lambs."
"This happened to be an African-American man who was very -- a person at the rally, who was very, very incensed at the fact that somebody, a protester, would be wearing a Ku Klux Klan outfit," Trump said of Pettway, on "This Week."
Trump added that "we don't condone violence," but complained that protesters are "stopping our First Amendment rights."
"When signs are put up, lifted up with tremendous profanity on them, I mean the worst profanity, and you have television cameras all over the place and people see these signs, I think maybe those people have some blame and should suffer some blame, also," he said.
Linda Rothman, 67, was also arrested for an unrelated misdemeanor assault and released.
Earlier this month, a Trump supporter elbowed a protester in the face as he was being escorted from the building. That man, John McGraw, 78, was later arrested and charged with assault