Defendant accuses Plaintiff of cheating in a competition. Plaintiff sues Defendant for defamation.
Plaintiff has heard rumours that Defendant is racist. Assuming these could be substantiated in some way:
Would it have been unhelpful for Plaintiff to bring this up in the lawsuit (given that Plaintiff did not do so)?
Would it be unhelpful for Plaintiff to bring this up later on eg in depositions or actual trial?
Information about a defendant’s character or past misdeeds are not generally admissible during a court proceeding.
It can be brought in to rebut testimony. If the defendant takes the stand and asserts that they never discriminated against anyone due to their nation of origin, then evidence they they have done so becomes relevant.
Bringing up rumors is rarely helpful in litigation. Rumors are hearsay, and therefore typically inadmissible.
assuming Hans some evidence of this possible racism: Would it have been unhelpful for Hans to bring this up in the lawsuit?
Although seemingly a stretch, the possible relevance of defendant's racism is twofold: (1) as supplementary proof of the defamation concept of actual malice, and (2) to attack defendant's credibility. The latter issue is in line with the answer George White posted. But, as always, factual details might lead to a different conclusion.
At the outset, it seems unlikely that defendant's racism is his ulterior motive in a context of competitions of intellectual skill where something highly valuable is at stake. If the plaintiff cannot bridge the gap, pursuing that argument could be perceived as a distracting tactic. A defendant might be overtly racist, but that does not automatically prove a particular state of mind in regard to defamatory falsehoods.
Would it be unhelpful for Hans to bring this up later on eg in depositions or actual trial?
It depends on procedural constraints and litigation strategy, as explained in the last paragraph in this other answer.
