The most common and most likely answer to this crossword clue is the 10 letter word DEFLECTING
I've seen this crossword clue in The Times
D
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Buddy explains!

The straight part
We know that "Deviating from course" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case deviating from course = deflecting.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 DEFLECTING mean?
DEFLECTING verb- To make (something) deviate from its original path.
- (ball games) To touch the ball, often unwittingly, after a shot or a sharp pass, thereby making it unpredictable for the other players.
- To deviate from its original path.
- To avoid addressing (questions, criticism, etc.).
- To divert (attention, etc.).