The most common and most likely answer to this crossword clue is the 4 plus 3 letter word LEAD OFF
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More clues leading to the result LEAD OFF
Buddy explains!

The straight part
We know that "set in motion" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case set in motion = lead off.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 LEAD OFF mean?
LEAD OFF noun- The first batter in the batting order.
- The first batter of an inning.
- The short distance that a player stands away from their current base.
- Beginning something by leading the way.