Former KYGO morning show host David Mueller, known professionally as "Jackson," said his right hand, in a closed fist with the palm down, came into contact with part of Swift's body.
"I felt what seemed to be a rib cage or ribs," Mueller said on the first day of testimony.
Swift's attorney, in earlier opening statements, said Mueller is only suing her for money and fame. But an attorney for the ex-radio host countered by arguing that Swift had recklessly ruined his radio career by falsely accusing him of inappropriate touching.
Mueller was fired days after the incident. In 2015 Mueller sued Swift, her mother Andrea Swift and her radio promotions director Frank Bell, claiming that the touching allegations are false. His suit argues that they pressured KYGO to fire him and that he lost his job because of the false accusations. Mueller is seeking $3 million in damages.
Swift, who was 23 at the time of the incident, countersued Mueller, accusing him of "reaching under her dress and grabbing her bottom" as they posed for a photo. Her suit argues that KYGO terminated Mueller after its own independent investigation.
The case is another variation on the "he said-she said" nature of high-profile sexual assault allegations. Attorneys for Swift, one of the most powerful celebrities in the world, argued in opening statements that Mueller was using her notoriety and fame for his own gain.
"He wants you to give him a payday," Doug Baldridge, Swift's attorney, told the jury of two men and six women. "His motivation is money, calling attention to himself, and getting revenge on his boss."
A 'reckless' accusation?
The photo of that meet-and-greet, which was leaked last year and shown in court on Tuesday, will be a central piece of evidence in the trial. The photo shows Mueller with his hand hidden from view near Swift's lower back.
Gabriel McFarland, Mueller's attorney, said the photo was "awkward" but did not show any inappropriate, under-skirt touching as Swift has alleged.
"If you look at that photo, his hand is not underneath her skirt. It's not ruffled, rumbled, affected in any form or fashion," he said.
The accusation of misconduct "was careless, it was reckless and it was part of in many ways what has destroyed Mr. Mueller's life," said McFarland.
McFarland also suggested that Mueller may have been a victim of mistaken identity and that Swift might be confusing him with another man who was there.
But Baldridge, Swift's attorney, said the pop star was sure it was Mueller who touched her. Baldridge also argued that Mueller had repeatedly changed his story and had destroyed evidence in the case leading up to trial.
He said Swift had been part of thousands of meet-and-greets, but had never had an incident like what happened with Mueller.
Swift, her mother and Bell are expected to testify. In court Tuesday, Swift wore a black-and-white checked dress with a collar and black tights and carried a beige handbag. She wore bright red lipstick and had her light brown hair pulled back in a bun with full bangs.
Taylor Swift's counter-lawsuit argues that the case will "serve as an example to other women who may resist publicly reliving similar outrageous and humiliating acts." Her suit also claims that any money recovered from the case will be donated to charitable organizations dedicated to protecting women from acts of sexual assault.
Mueller: 'I want to clear my name'
On the stand, Mueller described his short meeting with Swift in 2013. Mueller and his girlfriend at the time, Shannon Melcher, complimented Swift and then posed for a photo, he testified.
"[Swift] put her right arm around Shannon, pulled her towards her, and turned toward the photographer," Mueller said.
"I immediately started moving to get into the picture," he said.
That's when their hands and arms touched at Swift's rib cage, he said.
After the photo was taken, Taylor thanked them and she and Mueller shook hands, he testified. He said that his hand did not touch her butt and that he did not touch her inappropriately.
A short time later, Mueller was approached by a security guard who accused him of inappropriately grabbing Swift, which he denied. He was kicked out of the concert and told he was banned for life from Taylor Swift shows, he said.
The next day, his bosses told him he was suspended without pay amid an investigation. He was fired a day after that, he testified.
McFarland asked Mueller if his hand was underneath Swift's skirt, referring to the meet-and-greet photo shown on monitors in the courtroom.
"Absolutely not," Mueller said.
Mueller testified that he recorded the June 3 conversation with his bosses on an older model iPhone. He transferred the file to a laptop after phone stopped working properly but he accidentally spilled coffee on the computer.
Store technicians couldn't recover the full recording from the laptop, he testified. Later, a backup external also failed, he said.
Mueller said he did send McFarland 19 audio clips cut from the full recording.
He denied Baldridge's claim that he destroyed evidence and repeatedly changed his story.
This has "cost me my career, the thing I love to do .... It's been hard on my family and hard on my friends," Mueller said. "I want to clear my name."
Mueller: 'She forgot me'
During cross-examination, Baldridge again accused Mueller of trying to get rich off of Swift. Swift never initially publicized the incident, and when she filed her counter-suit, she had no reason to falsely accuse Mueller because she had never met him before, Baldridge said.
Mueller's suit didn't seek a specific monetary amount but an expert retained by the ex-radio host determined that nearly $3 million was a fair compensation for damages.
Baldridge said shock jocks like Howard Stern make a lot of money. "You'd like to make the kind of money he does," Baldridge asked Mueller, who has claimed his show is family-friend.
"I'm not interested in Howard Stern money," Mueller said.
Baldridge asked Mueller if Swift was the one who fired him. Mueller answered no.
Baldridge also referenced Mueller's description of Swift in a court deposition as cold and standoffish when they met. Hearing that, Swift sat up in courtroom. She looked disgusted. The pop star scribbled a note on a yellow Post-it and passed it to one of her attorneys.
Mueller said he drew that conclusion because Swift didn't welcome him into the photograph and paid more attention to his girlfriend.
"She didn't acknowledge me when it was time to pose for the photograph," Mueller testified.
Baldridge asked Mueller if he felt invisible at that moment.
"She forgot me," Mueller said.
Baldridge will continue cross examining Mueller on Wednesday.