Declare Mick is, over all, a free spirit (8)
I believe the answer is:
maverick
'all a free spirit' is the definition.
I can't judge whether this definition defines the answer.
'declare mick is over' is the wordplay.
'declare' becomes 'aver' (averring is a kind of declaring).
'is over' is an insertion indicator.
'aver' put inside 'mick' is 'MAVERICK'.
Can you help me to learn more?
(Other definitions for maverick that I've seen before include "Renegade" , "Unorthodox type" , "Unconventional person or unbranded calf in America" , "Unbranded animal or person of independent thought" , "Unpredictable sort of person" .)