I can upset a clergyman - but it's not right (10)
I believe the answer is:
inaccurate
'it's not right' is the definition.
(I've seen this before)
'i can upset a clergyman' is the wordplay.
'upset' shows that the letters should be reversed in order.
'a clergyman' becomes 'curate' (curate is a kind of clergyman).
'can' in reverse letter order is 'nac'.
'i'+'nac'+'curate'='INACCURATE'
'but' acts as a link.
(Other definitions for inaccurate that I've seen before include "Unreliable" , "wrong" , "not hitting all the right notes?" .)