They found Solo intoxicated and upset, saw injuries on her nephew and her sister, and arrested her after speaking with those present and determining that she was the primary aggressor, the release said.
She was booked into jail for investigation of two counts of fourth-degree domestic violence assault, and she was expected to remain in custody until an appearance Monday at Kirkland Municipal Court.
A telephone number listed for her was not accepting incoming calls Saturday, and the voice mail for a listing at the sister's home was full.
The sister was not identified by police, but in her memoir, Solo writes that she has a half sister named Terry.
Solo, 32, has won two Olympic gold medals for the U.S. women's national team. She also plays with the Seattle Reign of the National Women's Soccer League.
"We are aware of the situation with Hope and are now gathering information," the Reign posted on the team's Twitter feed.
In 2012, she married former Seattle Seahawks tight end Jerramy Stevens. He was arrested just before their wedding for investigation of assault after a disturbance involving her, but he was not charged. Maybrown represented Stevens in that case.
Solo said soon afterward that there never was an assault and that she and her new husband were happy.
"It's unfortunate what the media can do to judge before the facts are out there. It's hard to see, but it's a hard truth, and it's part of life," she said then. "I'm happy. I'm happily married. I would never stand for domestic violence. I've never been hit in my life."
In her last appearance for the U.S., Solo recorded her 71st career shutout, a 1-0 victory over France on June 14 in Tampa, Florida. She sat out the team's game against France on Thursday night in Connecticut.
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