Taking someone to court is different from not having a case thrown out, let alone winning. And yes, there are different requirements, particularly with celebrities and public officials.
The big things that need to be proven is that it's a lie and it either hurt the person financially or emotionally.
Jesse Ventura's case against Chris Kyle is a good example. He was a public figure, but he was able to show that Kyle lied. It wasn't about Kyle knocking out Ventura (which never happened either), it had to do with Kyle claiming that Ventura said '
we deserve to lose a few (soldiers).'
Because Ventura's team was able to prove that Kyle never knocked out Ventura and essentially the two weren't involved in anything...thus Ventura could prove that he never made that statement.
And Ventura was suing Kyle based on that statement because he could reasonably argue that it would cost him financially by hurting his reputation and possibly emotionally if it drew nutjobs that harassed Ventura based on Kyle's lie in his book.
The court eventually reversed the decision on appeal due to a technicality (Ventura's team wanted to make it clear that Kyle's estate wouldn't even pay a penny in a lawsuit as it would be paid by the publisher's insurance company and Ventura's team got the okay from the judge to point that out and the appeals court deemed that to be illegal to do despite getting the judge's okay).
With Elliott it's going to be a bit more difficult since the NFL didn't explicitly say that he abused a woman. And there's an employer/employee relationship with 'conduct' being involved. Elliott could certainly prove that this would hurt him financially, but it's a little tricky to claim that the NFL explicitly defamed Elliott.
YR