Losing, destroying, altering, or failing to preserve key evidence can directly reduce the value of a claim - or sink it entirely. When that happens, a court may limit defenses, exclude testimony, give the jury an unfavorable instruction, or impose other sanctions. In an injury case, that can affect proof of fault, the seriousness of harm, and the size of any damages award.

Spoliation is the destruction, significant alteration, or loss of evidence that should have been kept for a lawsuit or reasonably expected lawsuit. The evidence might be physical items, surveillance video, phone data, maintenance logs, emails, or medical records. A party does not always need bad intent to face consequences; negligent loss of evidence can still matter if it prejudices the other side. Courts focus on whether the evidence was relevant, whether there was a duty to preserve it, and how much the loss harms a fair hearing.

In practice, spoliation issues often arise early. After a crash, for example, a vehicle may be repaired before it is inspected, or video from a loading dock may be overwritten. That is why lawyers often send a preservation letter quickly.

In Massachusetts, courts may address spoliation through evidentiary remedies and other penalties, including under Massachusetts Rule of Civil Procedure 37. Massachusetts also recognizes that a jury may draw an adverse inference in appropriate cases, as discussed in cases such as Keene v. Brigham & Women's Hospital, Inc. (2003).