Testifying at a hearing on Patricia Driscoll's request for a no-contact order, Busch said she came uninvited and unannounced to his motorhome at Dover International Speedway in September, a week after he broke off their relationship. He said she demanded that he tell her son to his face that their relationship was over.
Driscoll, 37, testified a day earlier that Busch choked her and smashed her head into the bedroom wall three times and that she still fears for her safety.
"I don't know what he's capable of doing," she said.
Busch, 36, said that while the two were in his bedroom, he again asked her to leave, for what he said was the fifth time.
"I took my hands and cupped her cheeks and I looked at her eye to eye and I said 'you need to leave.' I was defusing the situation," he said.
Busch's attorneys have denied the assault allegations, which are the subject of a separate criminal investigation by Dover police.
Busch was called to the stand by Driscoll's attorney, Carolyn McNeice. She did not ask him whether he smashed Driscoll's head against the wall.
"She just did not want to hear that denial," Busch attorney Rusty Hardin said after the hearing. Hardin will cross-examine Busch when the hearing resumes Jan. 12.
"He will explain in detail his side of it," Hardin said.
Busch did offer some details, including that he was naked the entire time that Driscoll and her son were in the motorhome.
The man known in NASCAR circles for a bad-boy image that has earned him the nickname "The Outlaw" also testified that he had been crying earlier that night while watching "Seven Years in Tibet," a 1997 movie starring Brad Pitt.
"It was a moving experience... It was a spiritual movie," Busch explained, adding that the movie led him to reflect on his own life. "There were some tearjerker moments."
In a text to Driscoll that night, Busch told her that he was crying, lying on the floor and didn't know "which way was up."
In another text that night, Busch told Driscoll "I don't love anything right now."
Driscoll testified that she became concerned about Busch after seeing the texts and went to check on him, thinking she and her son could comfort him.
Driscoll and Busch both testified about an angry exchange following a race in New Hampshire, one week before Dover. It resulted in him damaging a rental car and her driving off, leaving him stranded at a Boston airport. She also said she tried to reach out to Busch's mother after the New Hampshire race, saying Busch was drinking and struggling with depression.
Busch testified that he told Driscoll "bye forever" after New Hampshire but acknowledged sending a text nearly a month later hoping to talk to her.
Busch's attorneys have portrayed Driscoll as a scorned woman out to destroy his career. Driscoll runs a small Washington, D.C.-based defence consulting firm and is president of the Armed Forces Foundation, a non-profit for veterans,
The first witness called by Hardin on Wednesday was Michael Doncheff, who was hired earlier this year to drive Busch's motorhome and serve as a personal assistant to the couple.
He said Busch treated him well but had a temper at times. Busch often deferred decisions to Driscoll, who Doncheff said could be "high maintenance."
Doncheff said on the night of the motorhome encounter, Driscoll sent him a screenshot from her earlier text conversation with Busch. He said he thought it might be a good idea for Driscoll to drive to Dover.
Doncheff also said he believed Driscoll when she later told him Busch had assaulted her, even though she previously had made what he considered unbelievable statements.
The day before the New Hampshire race, Doncheff said, he noticed that Driscoll was moving gingerly and seemed very stiff. She told him that she had been picked up by a big man and slammed to the ground while helping round up illegal immigrants at the Mexican border, a story Doncheff considered "far-fetched."
Doncheff also recounted a time when Driscoll was involved in a dispute involving a NASCAR sponsorship issue.
"NASCAR is nothing," he quoted Driscoll as saying. "I take down foreign governments. I own Washington."
Doncheff also said Driscoll told him she was a "trained assassin" for the U.S. government.