The most common and most likely answer to this crossword clue is the 9 letter word REVERSING
I've seen this crossword clue in The Guardian
R
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Buddy explains!
The straight part
We know that "Changing direction" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case changing direction = reversing.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 REVERSING mean?
REVERSING verb- To turn something around so that it faces the opposite direction or runs in the opposite sequence.
- To turn something inside out or upside down.
- To transpose the positions of two things.
- To change totally; to alter to the opposite.
- To return, come back.
- To turn away; to cause to depart.
- To cause to return; to recall.
- To revoke a law, or to change a decision into its opposite.
- To cause a mechanism or a vehicle to operate or move in the opposite direction to normal.
- To change the direction of a reaction such that the products become the reactants and vice-versa.
- To place a set of points in the reverse position
- (of points) to move from the normal position to the reverse position
- To overthrow; to subvert.
- An act of reversal.