The most common and most likely answer to this crossword clue is the 11 letter word BACK-HANDER
I've seen this crossword clue in Financial Times
B
A
C
K
-
H
A
N
D
E
R
Buddy explains!
The straight part
We know that "a blow" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a blow = back-hander.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 BACK-HANDER mean?
BACK-HANDER noun- A glass of wine given out of turn, the bottle having been handed backwards.
- A blow with the back of the hand.
- A bribe, a secret payment.
- (racquet sports) A shot played backhand, a backhand stroke.
- A surfer who approaches a swell with the wave behind them ("on their backhand") rather than facing the wave ("on their forehand").