Most flexible result, one secured by chief.. (8)
I believe the answer is:
bendiest
'most flexible result one secured by chief' is the definition.
I can't judge whether this defines the answer.
'most flexible result one secured by' is the wordplay.
'most' means to remove the last letter.
'flexible' becomes 'bendy' (able to bend).
'result' becomes 'est' (I can't justify this - if you can you should give a lot more credence to this answer).
'one' becomes 'i' (Roman numeral).
'secured by' is an insertion indicator (inserted letters are held or secured).
'bendy' with its final letter taken off is 'bend'.
'bend'+'est'='bendest'
'bendest' placed around 'i' is 'BENDIEST'.
Can you help me to learn more?