The concept of duty of care is crucial in negligence law, where a defendant must prove that they did not breach their duty to prevent harm to the plaintiff. In the given case study, Essendon Football Club failed to administer supplements to its professional athletes according to the World Anti-Doping Authority's requirements, resulting in players suffering loss of sponsorships, income, and reputation. As a result, the court fined the club $200,000 for breaching occupational health and safety laws in Victoria. The case highlights the importance of demonstrating duty of care in negligence claims.