the.com/foul play

means Underhanded or violent wrongdoing — especially suspected treachery behind a death or disappearance.

from Foul here is the old sense of 'dirty, offensive against rules,' the same root that gives us foul in sports and foul-smelling. 'Play' comes from the notion of a game governed by rules — fair play versus foul play. The pairing dates back centuries, originally meaning dishonest dealing in general, long before it narrowed into the go-to phrase for 'someone may have been murdered.'