Vicarious liability holds that when an employee is negligent and causes damage in the course of work, the employer is held liable. What if the "work" itself is negligent, and the damage brought about by negligence harms the very person hired for the negligent act?
For example, let's assume that Fred hires Barney to stage a fake attack during a self-defense class so that Fred can demonstrate a self-defense technique. Barney is therefore paid to act as Fred's attacker, and they have agreed on a safe plan to conduct this training session. None of the students are informed of this and it hasn't happened in the class before.
In the next lesson, Barney storms in through the open door and attempts to attack Fred with a training knife. One of the students, Uriah, intervenes and severely injures Barney due to thinking the sudden attack without warning is real. Fred neither injures nor is himself injured.
While I don't think Uriah would be liable (as a reasonable person would think Barney is a real attacker), would Fred be liable to Barney? Would the fact that Fred and Barney were both involved in a negligent plan be a factor?
Note: The United States is the jurisdiction, but various jurisdictions within the United States would factor in contributory negligence vs. compensatory negligence. I would be interested in hearing how both philosophies would play into the above scenario.