Defending himself against charges he lacks the energy to serve in the White House, Republican presidential candidate Ben Carson shared some anecdotes from his rough-and-tumble youth. “I am soft-spoken,” Carson told NBC’s "Meet the Press" in an interview broadcast Sunday morning. “I do have a tendency to be relaxed. I wasn’t always like that. There was a time when I was, you know, very volatile. But, you know, I changed.”

“As a teenager, I would go after people with rocks and bricks and baseball bats and hammers,” the retired neurosurgeon said. “And of course, many people know the story when I was 14 and I tried to stab someone. And, you know, fortunately … my life has been changed. And I’m a very different person now.”

Carson, who grew up poor in Detroit before becoming a world-renowned surgeon, has opened up about these incidents before. The person he tried to knife was his friend. And the recipient of the hammer attack threat was his mother.

Donald Trump, the national front-runner for the Republican presidential nomination, has ramped up his criticism of Carson as the latter has made steady polling gains. Two recent polls indicated Carson ahead of Trump in Iowa for the first time, by margins of 8 and 9 percentage points.

On Friday, the real estate mogul bashed the surging candidate at a rally in Miami.

“Ben Carson is super-low energy, right? He’s super low,” Trump said. “Super-low energy. We need tremendous energy. We need tremendous energy.”

At the same event, Trump pretended to read a headline. “Donald Trump falls to second place behind Ben Carson,” he said. “We informed Ben, but he was sleeping.”

Trump kept up the barrage of criticism on Twitter Sunday morning.

In the interview, Carson avoided direct criticism of Trump, saying he did not want to “get into the mud pit.”

When asked about abortion, the candidate compared the practice to slavery.

“During slavery, a lot of the slave owners thought that they had the right to do whatever they wanted to that slave. Anything that they chose to do. And, you know, what if the abolitionist had said, you know, 'I don't believe in slavery. I think it's wrong. But you guys do whatever you want to do'? Where would we be?"

He also said he does not support exceptions for rape and incest.

Last year, Carson compared the Affordable Care Act to slavery.