Legal Definitions - Mansfield rule

The Mansfield rule is a legal doctrine that prevents jurors from testifying or providing affidavits about their own misconduct to challenge a verdict. This rule ensures that jury verdicts are final and discourages losing parties from attempting to delve into the confidential deliberations of the jury room. It was first announced in 1785 by Lord Mansfield.

The Mansfield rule is a legal principle that generally prohibits jurors from testifying or providing affidavits about their own misconduct or internal deliberations to challenge a verdict they have already delivered. The primary purpose of this rule is to protect the finality and integrity of jury verdicts. It ensures that the jury's decision, once rendered, is respected as the definitive outcome of their deliberations, rather than being subject to endless scrutiny based on individual jurors' post-verdict accounts of what happened in the jury room. This helps prevent losing parties from attempting to overturn verdicts by probing the private discussions and thought processes of jurors.

• Example 1: Allegations of Juror Bias During Deliberations

  Imagine a civil trial where the jury awards a large sum of money to the plaintiff. After the verdict, one of the jurors, Juror A, contacts the losing defendant's attorney. Juror A claims that another juror, Juror B, repeatedly made disparaging and biased remarks about the defendant's company throughout the deliberations, suggesting that Juror B had a personal vendetta rather than evaluating the evidence fairly. The defendant's attorney wants to use Juror A's testimony to argue for a new trial, claiming juror misconduct.

  How the Mansfield rule applies: The Mansfield rule would likely prevent Juror A from testifying about Juror B's biased comments made during the private deliberations. These comments, while potentially problematic, are considered internal to the jury's decision-making process. Allowing such testimony would open the door to challenges based on the subjective experiences and opinions exchanged within the jury room, undermining the finality of the verdict.

• Example 2: Juror Claiming Disregard for Evidence

  In a high-profile criminal case, the jury convicts the defendant. A few days later, one of the jurors reaches out to the defense team, stating in an affidavit that she personally ignored much of the complex financial evidence presented during the trial. She admits that she had already formed an opinion about the defendant's guilt based on news reports she read before the trial, despite the judge's explicit instructions to only consider evidence presented in court. The defense attorney seeks to use this juror's affidavit to argue for a new trial due to juror misconduct.

  How the Mansfield rule applies: The Mansfield rule would typically prevent the court from considering this juror's affidavit. Her claim about her own internal thought process and failure to follow instructions during deliberations is precisely the type of internal jury misconduct that the rule aims to shield from post-verdict scrutiny. To allow such a challenge would encourage jurors to second-guess their own decisions and potentially reveal the private mental processes of the jury.

• Example 3: Juror Misunderstanding Legal Instructions

  Following a complicated patent infringement trial, the jury finds the defendant liable. One juror later tells a friend that she and several other jurors were confused by the judge's instructions regarding the definition of "prior art" and that if they had understood it correctly, their verdict might have been different. The defense learns of this conversation and attempts to introduce an affidavit from this juror to challenge the verdict, arguing that the jury did not properly apply the law due to a misunderstanding.

  How the Mansfield rule applies: The Mansfield rule would generally prevent the court from accepting such testimony. A juror's claim of misunderstanding legal instructions during deliberations is considered an internal matter of the jury's collective decision-making process. Allowing jurors to challenge a verdict based on their subjective interpretation or misunderstanding of the law after the fact would create instability in the judicial system and invite constant challenges to jury verdicts.