Leader of infantry escorted back, carrying a standard (5)
I believe the answer is:
ideal
'standard' is the definition.
(as in an ideal or optimal standard)
'leader of infantry escorted back carrying a' is the wordplay.
'leader of' suggests taking the first letters.
'escorted' becomes 'led' (to lead someone somewhere is to escort them).
'back' says the letters should be written backwards.
'carrying' is an insertion indicator.
The initial letter of 'infantry' is 'i'.
'led' backwards is 'del'.
'del' placed around 'a' is 'deal'.
'i'+'deal'='IDEAL'
(Other definitions for ideal that I've seen before include "example" , "superb specimen" , "A deli (anag.)" , "Consummate" , "principle to be aimed at" .)