"Foul play" refers to dishonest or unacceptable behavior, particularly related to a crime or misconduct, such as cheating, lying, or hurting someone. Full definition
The idea of having 4 children die through natural circumstances is so horrifying that it is much easier for human nature to believe that there was foul play involved. (housegoeshome.com)
Rule 12 states that a player is given a red card if he commits serious foul play or for violent conduct. (justarsenal.com)