And now...martial arts:
Martial arts teachers’ liability:
Under the Theory of Agency, the principal is liable for unlawful acts which he causes to be done through an agent.
There are three possible ways in which a martial arts instructor might be held liable as the principal for the unlawful acts of his students, as agents.
First, if the instructor appears to ratify or approve of unlawful conduct, he may be held liable for the commission of such acts. Thus, a dojo which encourages the use of excessive force, or lethal force in inappropriate situations may be seen to ratify and approve of unlawful conduct.
Similarly, an instructor who continues to teach a student who has abused his knowledge may be held responsible, if not liable, for subsequent torts.
Second, an instructor may be held liable for having entrusted a student with ‘an extremely dangerous instrumentality’. "[W]hen an instrumentality passes from the control of a person, his responsibility for injuries inflicted by it ceases. However, when an injury is caused by an exceptionally dangerous instrumentality, or one which may be dangerous if improperly used, a former owner or possessor may ... be charged with responsibility for [its] use...." The implications for instructors who teach potentially lethal techniques is clear.
Finally, an instructor may be liable for harm to the student or other parties as a result of negligent instruction. Anyone who holds himself out as an expert capable of giving instruction is expected to conform to the standards of his professional community. Thus, any instructor who, by his own negligence, fails to provide, teach and require adequate safe-guards and supervision, may be liable for any resulting injury.
Think about this a lot.