A more thorough explanation:

A retrial is a new trial of a case that happens after a previous trial has ended. It is done to re-examine some or all of the matters from the concluded trial. A party files a motion for a new trial, and a court may grant a retrial if there was a significant error of law, a verdict going against the weight of the evidence, irregularity in the court proceeding, jury or prosecutorial misconduct, newly discovered material evidence, or improper damages.

• U.S. v. Doyle: The Seventh Circuit granted a retrial based on prosecutorial misconduct. The prosecutors failed to disclose material exculpatory information which was favorable to the defense as they were bound to and where they failed to provide the defense with evidence relating to the credibility of prosecution witnesses.
• Payne v. Jones: The Second Circuit remanded for a retrial on damages. The Court found punitive damages of $300,000 for officer’s use of excessive force improper, emphasizing judges’ familiarity with the legal system and verdicts to justify the Court’s reduction in the jury’s punitive damage award.
• U.S. v. Eads: The Seventh Circuit explained that for federal criminal cases, for a criminal defendant to receive a retrial because of newly discovered evidence, the defendant must provide evidence that “(1) came to his knowledge only after trial;  (2) could not have been discovered sooner through the exercise of due diligence;  (3) is material and not merely impeaching or cumulative;  and (4) would probably lead to an acquittal in the event of a retrial.

These examples illustrate how a retrial can be granted for various reasons, such as prosecutorial misconduct, improper damages, or newly discovered evidence. In each case, the court found that there was a significant error in the previous trial that warranted a new trial to be held.