The most common and most likely answer to this crossword clue is the 5 plus 2 letter word KNOCK ON
I've seen this crossword clue in The Daily Telegraph
K
N
O
C
K
O
N
More clues leading to the result KNOCK ON
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 = knock on.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 KNOCK ON mean?
KNOCK ON noun- A foul in which a player knocks the ball forward.
- Resulting as an indirect effect.