The most common and most likely answer to this crossword clue is the 5 letter word COXES
I've seen this crossword clue in The Guardian
C
O
X
E
S
More clues leading to the result COXES
Buddy explains!

The straight part
We know that "Lightweight directors" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lightweight directors = coxes.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 COXES mean?
COXES noun- A coxswain of a boat, especially of a racing crew.