Commotion after prisoners start to trash building (12)
I believe the answer is:
construction
'building' is the definition.
(synonyms)
'commotion after prisoners start to trash' is the wordplay.
'commotion' becomes 'ruction' (synonyms).
'after' is a charade indicator (letters next to each other).
'prisoners' becomes 'cons'.
'start to' suggests taking the first letters.
The first letter of 'trash' is 't'.
'cons'+'t'='const'
'ruction' after 'const' is 'CONSTRUCTION'.
(Other definitions for construction that I've seen before include "Building; interpretation" , "Process of erecting buildings" , "Industry of erecting buildings" , "Act of building" .)