The most common and most likely answer to this crossword clue is the 8 letter word VILLAINY
I've seen this crossword clue in The Daily Telegraph
V
I
L
L
A
I
N
Y
More clues leading to the result VILLAINY
Buddy explains!

The straight part
We know that "foul play" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case foul play = villainy.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does VILLAINY mean?
VILLAINY noun- Evil or wicked character or behaviour.
- A wicked or treacherous act.
- Characteristic of a villain.