The most common and most likely answer to this crossword clue is the 5 plus 3 plus 5 letter word CALLS THE SHOTS
I've seen this crossword clue in The Daily Telegraph
C
A
L
L
S
T
H
E
S
H
O
T
S
Buddy explains!
The straight part
We know that "Wears the trousers/a film director does" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case wears the trousers/a film director does = calls the shots.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.