Set alight during campaign, it exploded (6)
I believe the answer is:
ignite
'set alight' is the definition.
(I've seen this before)
'during campaign it exploded' is the wordplay.
'during' indicates the answer is hidden within the clue.
'IGNITE' is hidden in the letters of 'campaign it exploded'.
(Other definitions for ignite that I've seen before include "Torch" , "Combust" , "Kindle Fire" , "Cause to catch fire" , "Spark off" .)