The most common and most likely answer to this crossword clue is the 10 letter word OV(ERSE)ER
I've seen this crossword clue in The Guardian
O
V
(
E
R
S
E
)
E
R
Buddy explains!

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 OV(ERSE)ER mean?
OV(ERSE)ER noun- One who oversees or supervises.
- A critic.