Now that the Fair Grounds has cancelled I have more time to reply . . .

This isn't my area of practice so take all of the following for what it is worth, which probably is not much.

The question of what would have to be shown would depend on whether the jockey could be considered a public figure. If the jockey is NOT a public figure, to prevail he would have to show the following:

(1) Defamatory language;
(2) about the plaintiff;
(3) which is published; and
(4) which causes injury to reputation.

If the jockey IS considered a public figure, he would have to establish, in addition to the above, that the defendant acted with "actual malice." "Actual malice" exists where the publication was made with knowledge of the falsity of the statements or with reckless disregard of their truth or falsity. That is a high standard and it is difficult for a public-figure plaintiff to prevail in a defamation suit.

I don't think than an intent to cause harm is technically an element of a defamation claim.