Maybe laddish guards shot some soldiers once (7)
I believe the answer is:
maniple
'some soldiers once' is the definition.
(subdivision of Roman soldiers)
'maybe laddish guards shot' is the wordplay.
'maybe laddish' becomes 'male' (like young males).
'guards' is an insertion indicator (inserted letters are guarded).
'shot' becomes 'nip' (synonyms).
'male' enclosing 'nip' is 'MANIPLE'.
(Other definitions for maniple that I've seen before include "company" , "foot soldiers" , "Garment" , "Some legionaries" , "church vestment" .)