The most common and most likely answer to this crossword clue is the 7 letter word MARSHES
I've seen this crossword clue in The Daily Telegraph
M
A
R
S
H
E
S
Buddy explains!
The straight part
We know that "where footballers may be found in Hackney" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case where footballers may be found in hackney = marshes.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 MARSHES mean?
MARSHES noun- An area of low, wet land, often with tall grass.