The most common and most likely answer to this crossword clue is the 10 letter word NITPICKING
I've seen this crossword clue in The Sunday Telegraph
N
I
T
P
I
C
K
I
N
G
Buddy explains!
The straight part
We know that "Critical" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case critical = nitpicking.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 NITPICKING mean?
NITPICKING noun- The painstaking process of removing nits (lice eggs) from someone's hair.
- (by extension) A process of finding or pointing out tiny details or errors, particularly if the pointed-out details seem insignificant or irrelevant to all but the finder.