Judy Huth, who is suing Mr. Cosby on sexual assault grounds in a civil case, took the stand in California to begin describing an encounter with the entertainer that took place decades ago.Judy Huth took the stand in Santa Monica on Monday to describe a moment in 1975 when, as a teenager, she said she met Bill Cosby in a California park where he was making a film.Days later, at his invitation, she said, she and her friend went along to his tennis club and then ultimately to the Playboy Mansion in Los Angeles.“It was an adventure,” Ms. Huth said. “We were kids. He was a celebrity.”But later that day, the man she had admired as a famous comedian molested her, she said, after taking her to an isolated room at the mansion. Ms. Huth said she was 16 years old at the time.Mr. Cosby has denied he sexually assaulted Ms. Huth or any of the other women who have come forward in recent years to accuse him of sexual misconduct. He has said any relationship was consensual.But Ms. Huth, 64, has sued Mr. Cosby for sexual assault, and her account, which was not finished on Monday, is the centerpiece of her case against the entertainer, which completed its fourth day of testimony. Ms. Huth testified that she and her friend had been impressed when they saw Mr. Cosby — along with other movie stars — in a park in San Marino on the set of the film “Let’s Do It Again.” According to her account, Mr. Cosby gave the two teenagers alcohol at a house where he was staying, telling them to drink if he bested them in a game of pool, and then asked them to follow him in a car to the mansion. The Sexual Assault Cases Against Bill CosbyAfter Bill Cosby’s 2018 criminal conviction for sexual assault was overturned, the first civil case accusing him of sexual misconduct has reached trial.The Civil Trial: Judy Huth has accused Mr. Cosby of assaulting her as a teenager. She sued in 2014, but the case had been on hold while he was criminally prosecuted.Criminal Conviction: In 2018, a jury found the disgraced entertainer guilty of drugging and sexually assaulting Andrea Constand at his home near 14 years earlier,His Release From Prison: After the Pennsylvania Supreme Court overturned the conviction, Mr. Cosby was released from prison on June 30, 2021.The Ruling: The conviction was overturned on the grounds that prosecutors violated Mr. Cosby’s rights by reneging on a promise not to charge him.“Are you girls ready for your surprise?” he said, according to Ms. Huth. “I had no clue what it could be,” she said. Her lawyers showed the jury a photograph of Ms. Huth standing with Mr. Cosby in the game room at the mansion, taken, she told the court, “before he molested me. It happened 15 minutes after.”Ms. Huth’s testimony was interrupted by the end of the court day before she was able to discuss what she has, in court papers for her case, accused him of doing: placing his hand down her pants and then forcing her to fondle him.The impact of that event, her lawyers have told the court, included depression and anxiety. She had experienced a happy childhood, she said, growing up in Temple City, Calif. But her lawyers said that the incident had derailed her and that she didn’t earn her high school diploma until she was 60.Mr. Cosby’s lawyers have disputed Ms. Huth’s account, suggesting that their meeting actually happened years later, when she was an older, and willing, visitor to the mansion who by her own account did not flee after the encounter but stayed on for hours, swimming in the pool and watching a movie.Ms. Huth’s lawsuit, filed in 2014, was largely on hold while prosecutors in Pennsylvania pursued Mr. Cosby, 84, criminally on charges that he had sexually assaulted Andrea Constand, a former Temple University employee.But Mr. Cosby’s 2018 conviction in that case was overturned last year by the Pennsylvania Supreme Court on due process grounds, and Mr. Cosby walked free after serving nearly three years of a three- to 10-year sentence.Mr. Cosby, flanked by two of his lawyers, outside his home in the Philadelphia suburbs after being freed from prison last year. Mark Makela/ReutersEarlier on Monday, Mr. Cosby’s lawyers had cross-examined Donna Samuelson, Ms. Huth’s friend who accompanied her to the mansion. She had told the court last week that Ms. Huth had been distraught after her encounter with Mr. Cosby but that Ms. Samuelson persuaded her to stay.Mr. Cosby’s defense tried to undermine the credibility of that account, suggesting that the two friends had coordinated their stories before Ms. Huth first went to the police in 2014. (Prosecutors ultimately declined to file criminal charges because the statute of limitations had passed.)But Ms. Samuelson said she had simply misremembered when she had initially reported to authorities that Ms. Huth was 15 at the time, not 16 as Ms. Huth now says.Mr. Cosby’s lawyers showed a layout of the game room at the Playboy Mansion and said that Ms. Samuelson had been wrong to say a person could access the bathroom only through an adjoining bedroom.Mr. Cosby’s lawyers also said it was impossible for Ms. Samuelson to have played the arcade game “Donkey Kong” there in 1975, as she has testified in a deposition. The game was not released until six years later.Ms. Samuelson said she meant that she had played a game like Donkey Kong.She denied that she and Ms. Huth had coordinated their accounts before Ms. Huth went to the police in 2014. “We were not putting anything together,” she said. “We were just telling our memories.”Jennifer Bonjean, a lawyer for Mr. Cosby, also brought up the subject of race in a way that suggested Ms. Samuelson was motivated to take down Mr. Cosby because he is Black. She said, for example, that Ms. Samuelson, in her pre-trial deposition, had described the décor of his house in Los Angeles as “jungly” and “African,” referring to the leaf print on the wallpaper.“It wasn’t atypical for people in your friend group to use racial slurs like the N-word,” the lawyer asserted.Ms. Samuelson said she never did that.“I am not racist,” she said.One of Mr. Cosby’s lawyers, Jennifer Bonjean.Lucy Nicholson/ReutersMr. Cosby’s lawyers have noted in court proceedings that Ms. Huth’s recollection of when her encounter took place has changed: While she initially said it had happened in 1974, when she was 15, she more recently concluded it was in 1975, when she was 16. The law in California classified a 16-year-old as a minor. In disputing Ms. Huth’s account, Mr. Cosby’s lawyers have suggested they met years after the time she said they did, when she was no longer a minor.Last week, Ms. Huth’s legal team introduced two other women who testified about encounters with Mr. Cosby. Kimberly Burr testified that she was 14 years old when he tried to kiss her in his trailer on the set of “Let’s Do It Again” in 1975 as well.Margie Shapiro testified that she was 19 that year when Mr. Cosby met her at the doughnut shop where she was working and invited her to the set of another movie he was filming in Los Angeles. Later that day, according to her testimony, she went to his house and then they went to the Playboy Mansion, where, she said, he drugged and assaulted her, an accusation that Mr. Cosby denies.Mr. Cosby is not expected to testify at the trial, having asserted his Fifth Amendment rights. But lawyers for Ms. Huth deposed him several years ago, and a portion of that testimony is expected to be presented in court before the conclusion of the trial, which is expected to last through the week. More