In every defamation case the First Amendment mandates an inquiry into whether a statement is "opinion" or "fact," and that only the latter statements may be actionable.
Respondent J. Theodore Diadiun authored an article in an Ohio newspaper implying that petitioner Michael Milkovich, a local high school wrestling coach, lied under oath in a judicial proceeding about an incident involving petitioner and his team which occurred at a wrestling match. Petitioner sued Diadiun and the newspaper for libel, and the Ohio Court of Appeals affirmed a lower court entry of summary judgment against petitioner. This judgment was based in part on the grounds that the article constituted an "opinion" protected from the reach of state defamation law by the First Amendment to the United States Constitution.
Are opinions constitutionally protected from defamation suits when they're sufficiently factual?
The Court holds that the First Amendment does not prohibit the application of Ohio's libel laws to the alleged defamations contained in the article. The privilege of "fair comment" was incorporated into the common law as an affirmative defense to an action for defamation. "The principle of 'fair comment' afforded legal immunity for the honest expression of opinion on matters of legitimate public interest when based upon a true or privileged statement of fact." Further, the assertion that the Petitioner committed perjury is sufficiently factual to be susceptible of being proven true or false, because one can look at his testimony to determine that. There are important social values that underlie the law of defamation that they court has acknowledged but this case holds the balance between that and allowing for free speech.