Teacher after clemency for army officer (13)
I believe the answer is:
quartermaster
'army officer' is the definition.
(quartermaster is a kind of army officer)
'teacher after clemency' is the wordplay.
'teacher' becomes 'master' (I've seen this before).
'after' means one lot of letters go next to another.
'clemency' becomes 'quarter' (I've seen this before).
'master' put after 'quarter' is 'QUARTERMASTER'.
'for' acts as a link.
(Other definitions for quartermaster that I've seen before include "Regimental officer responsible for accommodation, food etc" , "Person in charge of military supplies" , "Supply officer" , "petty officer, perhaps" , "Army officer responsible for administration" .)