Chastain v. City of Kansas City

What sanction did the court impose?

Appeal dismissed without reaching the merits for substantial failure to comply with Rule 84.04. No monetary sanction imposed. The opinion functions as an on-the-record judicial warning that citing 'AI Overview' or similar AI-generated search summaries is not legal authority and may itself trigger sanctions in subsequent Missouri appellate briefs.

Why does Chastain v. City of Kansas City matter for law firms using AI?

Chastain v. City of Kansas City is the Missouri appellate complement to Kruse v. Karlen. Where Kruse addressed AI-generated fabricated case citations and imposed a $10,000 frivolous-appeal sanction, Chastain addresses a different AI failure mode: citing AI-generated search summaries (Google’s ‘AI Overview’ feature) as if they were legal authority. The court treats both as Rule 84.04 violations, but Chastain is the first published Missouri opinion to draw the distinction.

The opinion’s most quotable line is the duty-to-verify framing: ‘Chastain had a duty to verify the accuracy of the AI results with legal authority and to supply the Court with such authority, not a simple “AI Overview.”’ Footnote 11 of the opinion folds in the broader sister-court line of cases on AI-induced sanctions, citing the principle that ‘using artificial intelligence to draft a legal document may lead to sanctions if the user fails to perform a critical review’ for fictitious authority. The court did not reach a Rule 55.03 or Rule 84.19 sanction analysis here (unlike Kruse, where $10,000 was awarded) because the procedural deficiencies under Rule 84.04 alone supplied a basis to dismiss.

The dispositive holding is narrow: Chastain’s amended brief ‘substantially fails to comply with Rule 84.04 and thus preserves nothing for our review. The appeal is dismissed.’ But the AI-related dicta is the part that travels. Western District Missouri firms can cite Chastain in any appellate matter where opposing counsel or a pro se litigant relies on AI-generated summaries instead of case law. The opinion is also useful in firm-internal training materials as the lead Missouri authority for the proposition that AI search summaries are not citations.

For managing partners, the practical implication is that Missouri’s Western District appellate panels are now actively reading briefs for AI-summary citations and treating them as a basis to dismiss. The volume of AI-summary citation in pro se filings is rising; Chastain is the published authority to cite when objecting to it.