For jury trials in Missouri state court, parties are required to use the appropriate Missouri Approved Instruction (MAI) for the claims and defenses submitted to the jury for determination. This is not necessarily a straightforward process. There are many instances in which there is not a specific MAI for a certain type of claim or defense. In those cases, the parties must typically craft a proposed instruction based on case precedent. Moreover, sometimes it is not clear which MAI should be used or to what extent an existing MAI should be modified to address the specifical factual or legal issues of a case.
If the jury is given an erroneous, confusing or inappropriate instruction it is possible for the court of appeals to vacate and reverse a jury verdict and order a new trial. This can be especially maddening after a lengthy trial which results in a friendly verdict. To reverse a jury verdict on appeal on the ground of instructional error, the party challenging the instruction must show that (1) the instruction as submitted, misled, misdirected or confused the jury and (2) prejudice resulted from the instruction. Flesher v. Pepose Vision, P.C., 304 S.W.3d 81, 90-91 (Mo. 2010).