Hit men: one coming after you! (9)
I believe the answer is:
successor
'one coming after you' is the definition.
(I've seen this before)
'hit men' is the wordplay.
'hit' becomes 'success' (as in a hit song).
'men' becomes 'OR' (military abbreviation for Other Ranks).
'success'+'or'='SUCCESSOR'
(Other definitions for successor that I've seen before include "one will take your place" , "Person who follows next in order" , "One taking over from another" , "Follower (in post)" , "One following another" .)