intervening cause

Definition from Nolo’s Plain-English Law Dictionary

An event that occurs after a party's improper or dangerous action and before the damage that could otherwise have been caused by the dangerous act, thereby breaking the chain of causation between the original act and the harm to the injured person. The result is that the person who started the chain of events may no longer be considered responsible for damages to the injured person since the original action is no longer the proximate cause.

Definition provided by Nolo’s Plain-English Law Dictionary.