Tennant alleges that Walton pinned her down in a Santa Monica hotel room in 2014, held her arms down and groped and sexually assaulted her as she begged him to stop.
Walton, who is now head coach of the Sacramento Kings, has denied the allegations.
In a press conference with her attorneys, Tennant described how Walton invited her up to his hotel room after she asked to meet to give him a copy of a book she had just written.
Walton was an assistant coach with the Golden State Warriors at the time, but the two had known each other for years, she said. She had known his wife through playing volleyball tournaments and had met him about 10 years ago at one of those events. They also worked together in 2013 while he was a basketball analyst at Time Warner and she was a reporter covering the Lakers.
Walton had written the book's introduction and she says she planned to give him a gift-wrapped copy.
She says she met him downstairs at his Santa Monica hotel while Walton was in town for a Warriors-Lakers game.
She says she was surprised when he invited her to talk in his hotel room. She was reluctant, but says he told her that his players were in the lobby and he didn't want to meet with her in front of them. Because she had known him for years, she said, she decided to go with him up to the room.
"Out of nowhere he got on top of me and pinned me to the bed," she said. "And held my arms down with all of his weight while he kissed my neck and my face and my chest. And as I kept asking him to please stop and to get off, he laughed at me."
"I continued to ask him to stop over and over again, without any use of my arms, because he continued to hold me down."
"I thought he was going to rape me."
After he finally let up, she said, she tried to leave the room and he jumped up and grabbed her from behind and again started kissing her neck.
He finally let her go and she left the room.
When asked why she waited so long to come forward, she said she was scared.
"When someone assaults you and you think you're going to be raped, coming forward is a scary thing. I have spent years now trying to deal with this."
When asked why Tennant had not filed a report with the Santa Monica police, her attorney, Garo Mardirossian, said because of the amount of time that had gone by, he believed it would be difficult to meet the standards for a criminal case.
"More often than not when you go to police a few years later, it's very difficult to put together a case where you have to prove beyond a reasonable doubt - the standard is much higher - so police departments are not very likely to get involved in a case this old at this time," Mardirossian said.
However, he did say he remained open to the idea of possibly filing a police report.
Walton has denied the allegations. His attorney, Mark Baute, released a statement saying: "The accuser is an opportunist, not a victim, and her claim is not credible."
The Lakers have noted that the allegations relate to a time when Walton was not working for the team and they had no knowledge of the accusations while he was the coach.
The Warriors said they just learned of the allegations Monday and declined further comment. The Sacramento Kings have also declined comment.
Meanwhile, a petition is circulating in the Sacramento area to remove the new head coach from his position.
See the full press conference with Kelli Tennant and attorney Garo Mardirossian here: