Objection, Kennemur! (Trial Expert Objection)

Kennemur (Kennemur v. State of California (1982) 133 Cal.App.3d 907) was about using a surprise expert opinion to challenge the other side’s expert at trial. The defense called an expert who said some tire tracks on the road belonged to a certain car. The plaintiff's expert, when asked earlier (at deposition), didn’t say who made the tire tracks and said that was someone else’s job. But then, at trial, the plaintiff tried to have that same expert say the tracks belonged to a different car. They argued this new opinion was just “impeachment” — basically saying it was okay to bring it up late without warning because it was just to challenge the other expert.

The court said no. They explained that just disagreeing with another expert’s opinion doesn’t count as “impeachment.” For an expert opinion to be considered true impeachment, the expert has to show that a basic fact that the other expert relied on is wrong, not just that the conclusion is different. So in Kennemur, if the plaintiff had shown, for example, that the photos the defense expert used were fake or from a different part of the road, that would have been impeachment.

What's the point? This case makes it clear that experts can’t just come to trial with new opinions they never said before if the other side didn’t get a chance to know about them during discovery. This is all about making sure trials aren’t surprises — everyone should know what the experts plan to say ahead of time so nobody gets blindsided. Courts want to avoid a “trial by ambush,” especially with experts.

This case is still important because it sets the rule that if you want to bring in an expert to knock down the basics of the other side’s expert opinion, that’s okay, but you can’t just bring a new opinion that contradicts it out of nowhere without proper notice.