The most common and most likely answer to this crossword clue is the 9 letter word SHORTAGES
I've seen this crossword clue in The Guardian
S
H
O
R
T
A
G
E
S
Buddy explains!
The straight part
We know that "when stocks are low" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case when stocks are low = shortages.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 SHORTAGES mean?
SHORTAGES noun- A lack or deficiency; an insufficient amount.