The most common and most likely answer to this crossword clue is the 9 letter word ACTIONING
I've seen this crossword clue in The Guardian
A
C
T
I
O
N
I
N
G
Buddy explains!
The straight part
We know that "Doing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case doing = actioning.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 ACTIONING mean?
ACTIONING verb- To act on a request etc, in order to put it into effect.
- To initiate a legal action against someone.