Trained gunners in reserve for rebellion (10)
I believe the answer is:
insurgence
'rebellion' is the definition.
(I've seen this before)
'trained gunners in reserve' is the wordplay.
'trained' indicates an anagram (to train can mean to grow something into a shape).
'in' is an insertion indicator.
'reserve' becomes 'ice' (I've seen this before).
'gunners' is an anagram of 'nsurgen'.
'nsurgen' going within 'ice' is 'INSURGENCE'.
'for' is the link.
(Other definitions for insurgence that I've seen before include "Rebellion" , "revolutionary activity" .)