Object — one associated with Hull — pocketed by doctor (5)
I believe the answer is:
demur
'object one' is the definition.
'demur' can be an answer for 'object' (to demur is to object to something). I am unsure of the 'one' bit.
'hull pocketed by doctor' is the wordplay.
'hull' becomes 'emu' (I can't justify this - if you can you should give a lot more credence to this answer).
'pocketed by' indicates putting letters inside.
'doctor' becomes 'dr' (abbreviation).
'emu' going within 'dr' is 'DEMUR'.
'associated with' acts as a link.
Can you help me to learn more?
(Other definitions for demur that I've seen before include "Politely disagree" , "Protest mildly, object" , "Raise scruples" , "Take exception (to)" , "Balk" .)