Set off, incite (5)
I believe the answer is:
spark
I believe this is a double definition.
'set off' is the first definition.
(synonyms)
'incite' is the second definition.
(I've seen this in another clue)
(Other definitions for spark that I've seen before include "Small electric flash" , "Fragment of a burning substance" , "Clever person" , "bit of fire?" , "Glowing particle" .)