The most common and most likely answer to this crossword clue is the 6 plus 7 letter word CAUGHT NAPPING
I've seen this crossword clue in The Daily Telegraph
C
A
U
G
H
T
N
A
P
P
I
N
G
More clues leading to the result CAUGHT NAPPING
Buddy explains!
The straight part
We know that "Taken by surprise" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case taken by surprise = caught napping.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.