Fine lieutenant protecting soldiers in disorder (7)
I believe the answer is:
ailment
'disorder' is the definition.
(ailment is a kind of disorder)
'fine lieutenant protecting soldiers' is the wordplay.
'fine' becomes 'ai' (I've seen this in other clues).
'lieutenant' becomes 'lt'.
'protecting' means one lot of letters goes inside another.
'soldiers' becomes 'men' (I've seen this before).
'lt' enclosing 'men' is 'lment'.
'ai'+'lment'='AILMENT'
'in' acts as a link.
(Other definitions for ailment that I've seen before include "Sickness" , "Physical disorder" , "Slight but persistent illness" , "I lament (anag.)" , "Complaint, affliction" .)