• automatism
• head injury
• medicolegal
• concussion

Automatism or automatic behaviour was originally described in the Hippocratic corpus in relation to sleepwalking and other nocturnal behaviours.¹ Despite its long history, this area of automatism remains confused and imprecise in the medical and legal literature. Within English common law, it is a fundamental principle that the intent (mens rea) and the act (actus reus) must occur together to constitute the crime.² As such, the absence of a mens rea means that the person at that point in time lacks the intent to commit a crime.

In the legal view, post-traumatic automatism is a form of “sane” automatism because it results from an external factor, for example, a blow to the head, rather than from a disease of the mind (which is responsible for “insane” automatisms).^{3, 4} As a legal defence under English law, if successful, post-traumatic automatism leads to acquittal rather than the judge deciding the disposal as in the case of insane automatism.⁵

In recent years, a number of cases of footballers appearing before disciplinary tribunals for striking and other charges have claimed in their defence that they suffered a prior concussive injury and at the time of the alleged incident were suffering from a “post-traumatic automatism” and as a result were not responsible for their actions. In one celebrated case in Australian football, this defence was successful and resulted in the sport's administrative body developing specific guidelines to outlaw this potential defence. This topic of post-traumatic automatism has only a limited amount of published information to guide practitioners, players, administrators, and lawyers and this paper seeks to establish appropriate medical guidelines in this area.