Somewhat hearty nuisance - one kicks off (6)
I believe the answer is:
atrial
'off' is the definition.
Although both the answer and definition are adjectives, I can't see how one could define the other.
'somewhat hearty nuisance one kicks' is the wordplay.
I cannot quite see how this works, but
'nuisance' could be 'trial' (both can mean something annoying) and 'trial' is found in the answer.
'one' could be 'a' (a thing is one thing) and 'a' is found in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for atrial that I've seen before include "Like main court" , "referring to Chambers?" , "Lariat (anag)" , "of the heart cavities" , "Like some courts" .)