Sack troublesome men I treat (9)
I believe the answer is:
terminate
'sack' is the definition.
('terminate' can be a synonym of 'sack')
'troublesome men i treat' is the wordplay.
'troublesome' indicates anagramming the letters.
'men'+'i'+'treat'='menitreat'
'menitreat' is an anagram of 'TERMINATE'.
(Other definitions for terminate that I've seen before include "Stop" , "Finalise" , "Put an end to, discontinue" , "Conclude" , "Close" .)