The most common and most likely answer to this crossword clue is the 8 letter word UPENDING
I've seen this crossword clue in The Daily Telegraph
U
P
E
N
D
I
N
G
Buddy explains!
The straight part
We know that "Turning over" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case turning over = upending.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 UPENDING mean?
UPENDING verb- To end up; to set on end.
- To tip or turn over.
- To destroy, invalidate, overthrow, or defeat.
- An act of overthrowing or turning over.