§ 2034.300.300

This section is what gives the rest of Chapter 18 its teeth. A party who plays by the exchange rules and then watches an opposing expert testify anyway, despite the opposing side having skipped a step, can object and force exclusion. If a party objects, and that objecting party made a complete and timely exchange under Section 2034.260, the trial court must exclude from evidence the opinion of any expert offered by a party who unreasonably failed to do what the chapter required.

Four failures trigger this consequence: not listing the witness as an expert under Section 2034.260, not submitting the required expert witness declaration, not producing the expert's reports and writings under Section 2034.270, or not making the expert available for a deposition under Article 3. The word unreasonably matters here; a failure explained by circumstances beyond the offering party's control, rather than by neglect or gamesmanship, does not automatically trigger exclusion. And this section is not the last word on its own operation: Section 2034.310 carves out situations where an undesignated expert can still testify, and Articles 4 and 5, covering augmentation motions and the court's discretion to manage the exchange, supply their own paths around a strict exclusion result.