Keeping Your Opponent’s Expert Witness in Their Lane: Guardrails for a Would-Be “Vehicle to Present a Factual Narrative”.

The article focuses on expert witnesses can certainly articulate the factual bases for their opinions, but they cross a line when they try to interpret communications and ascribe subjective intent to their authors. It mentions Federal Rules of Evidence provide limits, of course, but the case law can be inconsistent, and application of those theoretically straightforward rules can be as complicated as the testimony itself. It also mentions inadmissible facts or data to form an opinion.