The most common and most likely answer to this crossword clue is the 6 plus 2 letter word STRIKE UP
I've seen this crossword clue in The Guardian
S
T
R
I
K
E
U
P
More clues leading to the result STRIKE UP
- Initiate action on a plane, perhaps?
- Knock into the air and begin to play
- Industrial action finished, start playing
- Protest’s afoot: start singing!
- Start playing down tools, needing raise
- Assault over, start
- Apparently, pals begin to play?
- Stop working: finished: start playing!
- Instigate knight attached to the European Union to wear a belt
Buddy explains!
The straight part
We know that "Knock into the air/begin to play" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case knock into the air/begin to play = strike up.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.