Solo's half-sister Teresa Obert has told the KIRO7 news in Seattle about the alleged incident in June 2014 which saw Solo charged of two counts of domestic violence.
The charges were later dropped, but have now been reinstated following a local judge's decision in the wake of an appeal by prosecutors.
Solo denies the allegations, and claims she was the victim.
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With the charges now pending once more, the Oberts have told their side of an argument which took place between Solo and nephew Christian Obert, who had just turned 17.
The incident appears to have been sparked by Christian talking about a potential future in sport, something which Solo allegedly "began putting him down" for.
"It was just real stupidity and like, violent conversation for no reason," Christian Obert told KIRO 7, adding that he then asked her to leave.
"She had a big punch that sort of grazed me across the chin. And then I pushed her back into a filing cabinet. And from there, she lunged at me again and it went to the floor," alleged Christian.
Teresa Obert alleged that Solo kept on attacking from that point: "She tackled him again and grabbed his head and kept slamming him into the cement. Over and over. And his ear was bleeding, his nose was bleeding. So I got behind and I pulled with all my might to get her off of him....
"[Then] she started punching me in the face. Over and over again. And I spit out a piece of tooth."
As mentioned above, Solo denies all wrongdoing. After the charges were originally dropped in February she said: "I was a victim of domestic violence at the hands of my 17-year-old nephew, who is 6-foot-9, 280 pounds.. I was struck over the head and concussed, pretty severely. It was a very scary night."
Solo added that she is still "working through" her emotions in order to deal with the "traumatic events over the last year."
It is not the first brush with the law that Solo has been involved in. Earlier this year she was suspended from the national team for being in a van when her husband, former NFL star Jerramy Stevens, was arrested on suspicion of drink driving.