An example of breach of duty is a motor vehicle accident in which it's alleged that a defendant failed to obey the traffic laws under the applicable vehicle code. The duty to obey traffic laws is established by the vehicle code, and failing to stop at a red light or driving too fast is the breach of that duty.
In a negligence action, the breach is the failure to act with the level of care that a reasonable person, which is someone of ordinary prudence, would have exercised under the same or similar circumstances, according to Cornell University Law School. In the example of the car accident, the reasonable, prudent person would have obeyed all traffic laws. The breach usually consists of actions such as driving too fast for conditions or being inattentive or careless, but it can also consist of an omission when there is some duty to act. For example, a lifeguard has a duty to save a drowning person in a swimming pool. Not living up to the obligations of that job--a failure to act--would be the breach of the duty, which in this case was established by the job's responsibilities. In cases involving medical negligence, the duty is established by the required level of care and competency the medical professional should provide in the area of his expertise, and a breach of that duty is proved by showing that there was a failure to live up to those standards.