Ann Maurrer argued the trial court erred by permitting testimony and argument that, when taken together, allowed the jury to treat officers’ training and field-sobriety administration as proxy expert opinion about whether the defendant could safely operate a motor vehicle. Maurrer pointed to testimony where an officer described field-sobriety tests as designed to detect whether a person is ‘good to operate a motor vehicle’ and argued that linking training, test descriptions, and prosecutorial remarks risked converting lay testimony into an impermissible ultimate-issue opinion.

The justices asked whether the record supported a finding of substantial risk of prejudice, and whether the defense waived some remedial requests. Commonwealth counsel replied that officers’ testimony was factual, contextualized, and that the judge granted supplemental field-sobriety instructions the defense requested; the court heard extended colloquy on the choice of words such as ‘impaired’ versus ‘intoxicated,’ and whether the prosecutor’s opening and closing arguments improperly blended training and ultimate-issue assertions.

Why it matters: The court’s ruling will refine when police testimony about training and field-sobriety administration crosses the line into an expertized statement about driving ability and under what circumstances model jury instructions are required.

Outcome: Argument submitted.