An assumption of risk is a legal doctrine in personal injury cases, where the plaintiff's ability to recover is limited because they accepted the known dangers associated with an activity or product. Under the Federal Rules of Civil Procedure, assumption of risk is an affirmative defense, wherein an injured party has relieved the defendant of a duty of care.

A defendant must demonstrate that two things are true in order to make an assumption of risk claim:

1. That the injured party knew of the risk involved; and
2. That the injured party accepted the risk, either expressly or as implied by their words or conduct

There are two types of assumption of risk defenses:

1. Express assumption of risk — This is usually achieved through a signed waiver. As long as the waiver does not violate public policy, you cannot make a claim for your injuries if you have a contractual agreement giving up that right. For example, if you go skydiving, you'll likely have to sign a waiver which states that you understand that jumping out of a plane can result in serious injury or death.
2. Implied assumption of risk — This is achieved when your actions or behavior demonstrate that you were aware of the dangers of an activity and proceeded anyway. This is often the case in dangerous activities, or dangerous products such as power tools. A famous example of implied assumption of risk is Beninati v. Black Rock City, LLC (2009) 175 CA4th 650, wherein a man who was burned at the famous Burning Man Festival did not receive compensation because he assumed the risk of being burned merely by being at the festival.

In assumption of risk defenses, the plaintiff had to have been warned of, or been reasonably able to foresee, the specific danger inherent to the activity or product. For example, say your hands were burned by a chemical cleaning solution. If the product's labeling warned against ingesting the chemical, but did not warn against skin contact, then the product manufacturer would not be able to raise an assumption of risk defense.

Assumption of risk defenses are also commonly broken down into two further categories: primary and secondary.

In primary assumption of risk, the defendant does not owe the plaintiff any duty of care. A clear example is a football player who is injured while being tackled. They cannot sue the other player or team or the league for their injuries, as merely by agreeing to play they accepted the obvious, known risks involved in playing a high-contact sport.

In secondary assumption of risk, the defendant does owe the plaintiff a duty of care, and the defendant breached that duty, but the plaintiff encountered and was aware of that danger. For example, a contractor gives one of their employees a worn-down ladder to use, and warns the employee to be careful as the ladder may be dangerous. If the employee is injured while using the ladder, the employer could make a secondary assumption of risk defense. These cases are usually rolled into comparative negligence, where each party is liable for a portion of the damages.