Defendant Used ChatGPT

Defendant Used ChatGPT to Counter Expert Declaration: Artificial Intelligence Trends

The plaintiffs used a technical expert with four decades of experience to define a disputed term. The defendant used ChatGPT to counter his declaration.

That’s what happened in this patent dispute over softball bat technology between an inventor and a sporting goods company. The case related to U.S. Patent number 9,005,056 (filed July 30, 2013 and referred to as the “’056 Patent” throughout the ruling) regarding a bat, comprising five components, including a foam fitted within the tubular insert inside the tubular frame of the bat.

The parties disputed the definition of “foam” as used in the ‘056 Patent. The plaintiffs proposed that “foam” as referenced in the ‘056 Patent describes “a plastic material which includes air gaps.” They arrive at this description based on the declaration of their technical expert, Lawrence Fallon, who “has four decades of experience as an engineer; he began consulting for the sporting goods industry in 1990, predominately supporting baseball/softball equipment manufacturers and governing organizations…He co-founded the Baseball Research Center which became the official baseball and baseball bat test center for Major League Baseball, the National Collegiate Athletic Association, and the National Federation of High Schools.”


How did the defendant counter plaintiffs’ expert? The defendant used ChatGPT. As the ruling states: “In contrast, Pure Sports consulted ChatGPT to determine that the definition of ‘foam’ is ‘a substance with a structure characterized by the presence of numerous gas bubbles within a liquid or solid matrix.’”

As part of the plaintiffs’ reply, they said: “Pure Sports’s reliance on ChatGPT is defective ‘as ChatGPT did not exist in 2012,’ and ChatCPT [sic] ‘has recently been found to be an unreliable source of information, especially in legal proceedings.’”

That sentence included a footnote, which said: “The court agrees that thus far ChatGPT’s batting average in legal briefs leaves something to be desired. See, e.g., Mata v. Avianca, Inc., 2023 WL 4114965, at *15-17 (S.D.N.Y. June 22, 2023) (imposing sanctions on attorneys who relied on ChatGPT for research and whose ChatGPT queries resulted in fabricated legal authority which the attorneys submitted to the court without confirming the authority’s veracity).”

In rejecting the defendant’s use of ChatGPT, South Carolina District Judge David C. Norton stated: “courts are clear that ‘the ordinary and customary meaning of a claim term is the meaning that the term would have to a person of ordinary skill in the art in question at the time of the invention, i.e., as of the effective filing date of the patent application.’…The filing date of the ‘056 Patent was in 2013, well before the launch of ChatGPT in November 2022…Thus, the court would be taking its eye off the ball if it applied the ChatGPT definition in its review of extrinsic evidence.”


“Batting average”, “eye off the ball”, see what he did there? 😉

Judge Norton also cited the usefulness of expert testimony (Fallon), inventor testimony (the plaintiff Carl Pegnatori) and “a technical dictionary that predates the date the patent was filed”, which “defines ‘foam’ as ‘a dispersion of a gas in a liquid or solid.’” So, he found “that extrinsic evidence generally suggests that ‘foam’ as understood in the ‘056 Patent is defined as a plastic material in which gas is dispersed.”

Hat tip to Matt Linehan for the heads up about this story!

So, what do you think? Are you surprised that the defendant used ChatGPT to rebut the testimony of an expert with four decades of experience? Please share any comments you might have or if you’d like to know more about a particular topic.

Image created using Microsoft Bing’s Image Creator Powered by DALL-E, using the term “umpire throwing a player out of the game using watercolor”.

Disclaimer: The views represented herein are exclusively the views of the author, and do not necessarily represent the views held by my employer, my partners or my clients. eDiscovery Today is made available solely for educational purposes to provide general information about general eDiscovery principles and not to provide specific legal advice applicable to any particular circumstance. eDiscovery Today should not be used as a substitute for competent legal advice from a lawyer you have retained and who has agreed to represent you.


  1. “So, what do you think? Are you surprised that the defendant used ChatGPT to rebut the testimony of an expert with four decades of experience?”

    Not surprised at all, because with GPT there is as much FOMO as there is FOAM. (Aaaah.. I see what I did there!)

    In all seriousness, though: To defend the GPT-using lawyer, I suppose one could argue that the accumulated knowledge of all the sources GPT was trained on represent more than 40 person-years of expertise on the topic. So it doesn’t seem like an unreasonable place to start. But to me that’s the key: Start. Not end. GPT often “averages out” language and concepts, and what is needed here is a singular, strong voice or authority. In other words, I would still need/want to check GPT’s output with an expert.

    Then again, why not just go to the expert directly?

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