The most common and most likely answer to this crossword clue is the 9 letter word DECREASED
I've seen this crossword clue in The Times
D
E
C
R
E
A
S
E
D
More clues leading to the result DECREASED
Buddy explains!

The straight part
We know that "Dropped" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dropped = decreased.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 DECREASED mean?
DECREASED verb- Of a quantity, to become smaller.
- To make (a quantity) smaller.