Ultimately, buttock and lower back prodded by a couple of unknowns — one's an idiot (7)
I believe the answer is:
wazzock
'ultimately buttock and lower back prodded by a couple' is the definition.
I know nothing about this answer so I can't judge whether this works.
'unknowns one's an idiot' is the wordplay.
I cannot quite see how this works, but
'unknowns' could be 'zz' (two Z's - unknown values in algebra) and 'zz' is present in the answer.
'an' could be 'a' and 'a' is present in the answer.
The remaining letters 'wock' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'of' acts as a link.
Can you help me to learn more?
(Another definition for wazzock that I've seen is " Fool".)