The most common and most likely answer to this crossword clue is the 7 letter word IGNITED
I've seen this crossword clue in The Guardian
I
G
N
I
T
E
D
More clues leading to the result IGNITED
- Fired as a result of poor editing
- Set fire to coal, left out by daughter
- Editing suddenly fired up
- Set off crash dieting
- Sparked off furious editing
- Set off explosive without gel and died
- Light in the past – dieting worked
- Bad editing will get one fired up
- Dieting furiously getting fired up
- Fired for sloppy editing
Buddy explains!

The straight part
We know that "Set off" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case set off = ignited.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 IGNITED mean?
IGNITED verb- To set fire to (something), to light (something)
- To spark off (something), to trigger
- To commence burning.
- To subject to the action of intense heat; to heat strongly; often said of incombustible or infusible substances.