Legal Definitions - collateral matter

A collateral matter refers to a detail or issue in a legal case that is not directly central or essential to proving or disproving the main facts in dispute. Evidence related to a collateral matter would not be admissible on its own to establish a key element of the case.

The significance of identifying a collateral matter often arises when a witness testifies about a minor detail that turns out to be inaccurate. In such situations, the opposing party is generally not allowed to introduce additional evidence, such as calling another witness, solely to contradict the witness on that minor, irrelevant point. Instead, any challenge to the witness's credibility regarding a collateral matter must typically be made through cross-examination of that same witness.

Here are some examples:

• Car Accident Liability: Imagine a lawsuit stemming from a car accident where the central question is which driver was at fault. A witness testifies that they saw the accident happen and that the at-fault driver's car was a specific shade of green. Later, it is discovered that the car was actually blue. The exact color of the car is a collateral matter because it does not directly prove or disprove who was at fault for the accident, nor does it affect the driver's actions or the cause of the collision. The opposing side would not be permitted to call a paint expert or another witness solely to prove the car was blue, as that detail is not relevant to the core issue of liability. They could, however, question the original witness during cross-examination about their certainty regarding descriptive details.

• Breach of Contract: Consider a case where a company is suing a supplier for failing to deliver goods on time, breaching their contract. A witness for the supplier testifies that they personally called the company's representative on a specific date, say, October 10th, to confirm the delay. The company's records show the call actually occurred on October 12th. If the contract's terms do not hinge on the exact date of this particular phone call, and the crucial fact is simply whether the company was notified of the delay, then the precise date of the call is a collateral matter. The company could not bring in phone records or another witness just to prove the call was on October 12th, as that specific date isn't central to proving the breach. The focus remains on whether the notification happened, not the exact timing of a non-essential communication.

• Robbery Identification: In a criminal trial for robbery, a witness identifies the defendant as the person they saw fleeing the scene. During their testimony, the witness states that the robber was wearing a distinctive brand of athletic shoes. Later, it is revealed that the shoes the defendant owned and was wearing that day were a different, but similar, brand. If the overall identification of the defendant is strong and based on multiple factors (facial features, height, build, etc.), and the specific brand of shoes is merely a minor descriptive detail, then the exact brand of shoes could be considered a collateral matter. The defense would likely not be allowed to call a shoe expert to contradict the witness solely on the brand of shoes, as this detail does not directly prove or disprove the defendant's identity as the robber. The defense could, however, challenge the witness's observational skills during cross-examination.