AFAIK the plaintiff would have to show that it's not true. That wouldn't be anywhere near enough but would be a start. I think they would also have to show tha

AFAIK the plaintiff would have to show that it's not true. That wouldn't be anywhere near enough but would be a start. I think they would also have to show that either the defendant knew that it wasn't true, or was reckless about it. They also have to show that it was likely to be believed as a factual claim, so expressions of opinion or hyperbole are not defamatory. This isn't legal advice, just what I think from years of reading Popehat.