A principal type of practical joke (horseplay) injury is that caused by workmen trying to lighten the dull routine of work by playful funmaking. This involves the well established liability of a master for the torts of his servant done in the course and scope of the employment. It also involves the well-known limitation on respondeat superior that results when an employee in effect abandons his employment by making a detour from his business route, or by engaging in "a frolic of his own." This body of law has been greatly limited and changed (but not totally abolished) by enactment of statutes, such as workmen's compensation laws, that impose liability on the employer for almost anything done in the course and scope of employment. And, of course, old master-and-servant law still applies to many classes of cases which are excluded from (or not covered by) workmen's compensation rules.
Howard L. Oleck, Horseplay by Employees, 17 Clev.-Marshall L. Rev. 438 (1968)