The most common and most likely answer to this crossword clue is the 9 letter word DEFLECTOR
I've seen this crossword clue in The Times
D
E
F
L
E
C
T
O
R
Buddy explains!

The straight part
We know that "one providing diversion" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one providing diversion = deflector.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 DEFLECTOR mean?
DEFLECTOR noun- Something which deflects something else, especially a stream of fluid or particles.
- A diaphragm in a lamp, stove, etc. by which the flame and gases are brought together to improve combustion.
- A force field; an invisible barrier used as a protective shield.