Definition - What does Foul Play mean?
In criminal law, foul play is a euphemism for murder. As such, it includes an intentional act or acts that result in someone's death. These acts usually – but not always – involve physical violence, and can include shooting, stabbing, strangulation and poisoning.
Foul play or the lack thereof is determined through a criminal investigation.
Justipedia explains Foul Play
In cases where authorities are unsure if a death resulted from foul play, a thorough assessment of the corpse plays a significant role in the investigation. Performed by a coroner, this evaluation is called an autopsy, and is used to find clues pointing to the cause and manner of death.
For example, in cases where there are obvious injuries, the autopsy can determine whether they occurred prior to or after death and which, if any, were fatal. The autopsy can help pinpoint the time of death and the specific size and type of weapon used, if applicable.
Evidence identified during an autopsy can be used to show that the victim was choked to death. Information gathered during an autopsy can also determine if a sudden or otherwise inexplicable death stemmed from natural causes, disease or poisoning.
If an autopsy confirms the use of foul play, it is then up to the authorities to identify anyone who had reason and opportunity to commit the crime.