The most common and most likely answer to this crossword clue is the 5 letter word SLOSH
I've seen this crossword clue in The Daily Telegraph
S
L
O
S
H
More clues leading to the result SLOSH
Buddy explains!

The straight part
We know that "blow" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case blow = slosh.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 SLOSH mean?
SLOSH noun- A quantity of a liquid; more than a splash.
- A sloshing sound or motion.
- Slush.
- (of a liquid) To shift chaotically; to splash noisily.
- (of a liquid) To cause to slosh
- To make a sloshing sound.
- (of a liquid) To pour noisily, sloppily or in large amounts
- To move noisily through water or other liquid.
- To punch (someone).
- Backslash, the character \.