LONDON — In November 2007, a man pleaded guilty in a federal court in Dayton, Ohio, to illicit sexual conduct involving a 13-year-old girl. He was a judo coach, and the girl was a student he had trained closely and brought to international tournaments. Her name was given in court papers simply as “K.H.” or “the victim.”

K.H. was Kayla Harrison, who is now 22. On Thursday she won the first gold medal in judo for the United States. It was a remarkable victory for a woman who had faced far more in her young life than most can fathom and for a sport that is popular worldwide but has remained obscure in the U.S.

Of the Americans on the judo team here, Harrison was the favorite, though in the hurried gantlet of matches on Thursday she had to take on a Brazilian who was No. 1 in the world and, in the gold medal bout, a British woman, Gemma Gibbons, who was something of an underdog but still an overwhelming crowd darling. Some opponents in the 78-kilogram class Harrison threw to the ground; others she beat on points when the clock expired.

But there were more U.S. judo victories this week than just Harrison’s. In a lighter weight class, a young doctor’s receptionist named Marti Malloy won a bronze, the second Olympic medal ever for a U.S. woman in judo. A bruiser named Travis Stevens reached the semifinals in his weight class, knocking off the No. 1 seed along the way, and another American, Nick Delpopolo, who won his spot on the team by winning a single do-or-die match against a fellow American, reached the quarterfinals.

“This week we had our best judo performance ever,” said the U.S. judo coach Jimmy Pedro, a two-time Olympic bronze medalist himself who acknowledged that the United States had never been considered a powerhouse.

Harrison is simply the best on the team. It helps that she is also good-natured. And that she has a story she is not afraid to tell, a story that is jarring even for a sports press that can be nearly unhinged in its pursuit of the next inspirational tale.

Harrison has told her story before, first to USA Today only days after the indictment of Jerry Sandusky came down and the front pages were full of news about Penn State, sexual abuse and coaches who exploit their authority.

She said she felt it necessary to speak out so that others in her position could take heart.

She told it to newspapers and magazines, about how her coach had insinuated himself into the family, how sexual contact led to sexual intercourse over a period of years, on trips to Venezuela, Russia and Estonia, until she was 16. She told about finally revealing this to a friend (a firefighter who would become her fiance) and then to her mother, who smashed out the coach’s car windows with a baseball bat. (The former coach, Daniel Doyle, was sentenced to 10 years in prison and banned from the sport.)

And she told about how she was a mess — desperate, unhappy and ready to give up on everything — when within weeks her mother, Jeannie Yazell, took her from Ohio to study judo with Jimmy Pedro and his father, Jim Pedro Sr., at Pedro’s Judo Center in Wakefield, Mass.

“We just felt like she just had to get back to what she knew how to do,” Yazell said. “She could have control over what went on on the mat.”

The timing was auspicious, as it turned out. In 2005, a year after the Athens Olympics, the U.S. Olympic Committee met with the judo federation to discuss why the sport was struggling domestically.

There was a good system in place for fostering young talent, but nothing after that, and promising young competitors who triumphed on the junior circuit would lose their competitive edge as they became older. What came out of the meeting was a new program to spot and aggressively coach up-and-comers like Harrison.

So with that money and that program, she was forced out of bed in the morning, put on a nutrition program and pushed to lift more weights. She also began to win. She won gold at the 2008 junior world championships, then at the 2010 world championships, and came into the Olympics ranked No. 4.

About an hour after she had left the podium, the U.S. news media had mostly left and the British reporters crowded around Gibbons, their new silver medalist.

Harrison sat at a table fielding the last few questions, talking about her schedule in the coming days: She may take the EMT test to continue the process of becoming a firefighter, she said. She also wants to go to college and lead a normal life, having missed out on all the standard parts of American youth while she was grappling her opponents into submission on the mat.

“I think,” she said, “it’d be pretty cool to be a kid.”