Troop company undermanned, leaderless (6)
I believe the answer is:
cohort
'troop' is the definition.
(thesaurus)
'company undermanned leaderless' is the wordplay.
'company' becomes 'co' (abbreviation).
'undermanned' becomes 'short' (as in short-staffed).
'leaderless' means to remove the first letter.
'short' with its first letter taken off is 'hort'.
'co'+'hort'='COHORT'
(Other definitions for cohort that I've seen before include "Tenth part of a Roman legion" , "Group of similar people" , "Ancient Roman military unit" , "Group of people with a shared characteristic, age say" , "Unit of Roman soldiers - group of people of same age" .)