Greatness displayed by army NCOs (9)
I believe the answer is:
sergeants
'army ncos' is the definition.
I can't tell whether this definition defines the answer.
'greatness displayed' is the wordplay.
'greatness' can be anagrammed to 'SERGEANTS'.
Though, I am not clear how the anagram is indicated.
'by' acts as a link.
Can you help me to learn more?
(Other definitions for sergeants that I've seen before include "Greatness among NCOs" , "Greatness observed in NCOs" , "Odd greatness of these army and police ranks" .)