Ducks die off and fighters lose struggle (6)
I believe the answer is:
eiders
'ducks' is the definition.
(eider is a kind of duck)
'die off and fighters lose struggle' is the wordplay.
'die off' becomes 'eid' (I can't explain this - if you can you should give a lot more credence to this answer).
'and' says to put letters next to each other.
'fighters' becomes 'boxers' (boxer is a kind of fighter).
'lose' is a deletion indicator.
'struggle' becomes 'box' (boxing is a kind of struggling).
'boxers' with 'box' taken out is 'ers'.
'eid'+'ers'='EIDERS'
Can you help me to learn more?
(Another definition for eiders that I've seen is " Ducks with fine soft down".)