She says he lured her into his hotel room and forced himself on her.
He says he would never force himself on any woman.
Lawyers say in cases where it's one person's word against another's, it's a battle for credibility, with the onus typically on the accuser.
So in the case of a Nevada hotel employee accusing Steelers quarterback Ben Roethlisberger, the questions will be:
Why didn't the alleged victim go to the police?
Who else did she tell?
What is her past history?
How did she end up in his room?
Who is most believable?
For the plaintiff, the burden is huge.
"She's going to be the one who carries the day," said Michael O'Day, a former assistant district attorney turned defense lawyer, who's tried many of these cases. "It all comes down to credibility."
The question that has lingered in the thoughts of Pittsburghers and talk-show hosts for days is why the woman never sought out law enforcement to report that she was sexually assaulted.
According to the lawsuit, she reported the alleged assault to the chief of hotel security the next day.
But she still has never gone to the Douglas County Sheriff's Office to file a complaint.
"She should have been advised immediately by a lawyer to get to the prosecutor's office," Mr. O'Day said. "The lapse of time calls into question credibility and her motives, especially."
Defense attorney Caroline Roberto agrees not having a police complaint could be detrimental to the woman's claims, but she believes the man representing her, Calvin Dunlap, knows what he's doing.
"He's a former district attorney. He has intimate knowledge of that office and those investigators," she said. "He must have thought that if she waited eight months, they're not going to take the allegations seriously."
And having a bad result from a criminal case -- or no charges brought at all -- could make a civil claim that much harder to win, said Denver attorney John Clune, who represented the woman who accused basketball star Kobe Bryant of sexual assault.
But more than that, it's possible the woman chose not to go to law enforcement because she feared the loss of control that can come with a criminal investigation.
"While law enforcement and prosecutors have great concern for victims, they have a larger obligation to the community to make sure sex offenders are prosecuted," Mr. Clune said.
In a civil setting, the plaintiff's attorney is an advocate, working strictly for the victim.
Lisae C. Jordan, the director of the Sexual Assault Legal Institute in Maryland, doesn't think a victim's choice to not go to police is indicative of how strong her civil case might be.
"There are many much easier ways to make money than putting yourself through a civil trial and falsely accusing someone of a violent crime," she said.
Regardless of the woman's reasons for choosing not to go to police, all of the attorneys agree it will be a stumbling block for whomever might decide the case -- either a judge or jury.
"It's unfortunate because the reality is most sexual assault victims do not report to the police," Mr. Clune said.
But, he continued, "More often than not, it's very explainable in the victim's own words, why they didn't go to the police."
Mr. O'Day, who said these types of cases are not easy to prove, agreed that a believable witness can sway even the most cynical jurors.
"When the person comes into court, and they take the stand, and they look like they're telling the truth, it can be the end for the jury," he said.
When talking about credibility, Mr. O'Day said that the defense will focus on the woman's story and try to find even the smallest inconsistencies.
He would track down anyone that she confided in and compare what they were told.
More than that, the alleged victim must also be prepared to have her entire history -- both sexual and psychological -- torn apart.
"He can bring up almost everything he can to show her character or ability to tell the truth," Mr. O'Day said. "In the civil realm, you don't have rape shield laws."
The alleged victim likely won't have the same opportunity to turn the tables on Mr. Roethlisberger for any prior bad acts, unless there is a criminal conviction out there.
Another significant question for the case, Ms. Roberto said, is how the woman allegedly ended up in Mr. Roethlisberger's room.
According to the lawsuit, he complained that the sound system on the television in his room wasn't working properly, and he asked her to fix it.
"If she can corroborate why she went to the room, that would be helpful to her," Ms. Roberto said.
Otherwise, that question, too, will turn on credibility.
On that count, Mr. Roethlisberger has an automatic edge.
"Most sexual assault victims feel like no one's going to believe them in the first place," Mr. Clune said. "When you talk about someone who's a star athlete, that's got to be all the more intensified."
Paula Reed Ward can be reached at email@example.com or 412-263-2620.