foul play 
noun [mass noun]
1Unfair play in a game or sport: the referee sent off two players for foul play...
- Surely assisting the referee with decisions on foul play would assist the ref as well.
- The referee awarded only a penalty for the foul play, and the full-back remained on the field.
- This glorious sport must be freed from brutality and foul play.
2Criminal or violent behaviour, in particular when resulting in another’s death: the man appeared to have died as a result of a fall, and foul play was not suspected...
- No cause of death was given but foul play is not suspected.
- The circumstances of his death excited questions of foul play.
- Police in Northern Ireland have ruled out any foul play in Fulton's death.
Synonyms
criminal activity, crime, a criminal offence, villainy, murder, criminal violence, criminality
informal dirty deeds