Belief of immodest Hapsburg leader in Reformation (9)
I believe the answer is:
methodism
'belief' is the definition.
(Methodism is an example)
'immodest hapsburg leader in reformation' is the wordplay.
'leader' says to take the initial letters.
'in reformation' is an anagram indicator (I've seen this in other clues).
The initial letter of 'hapsburg' is 'h'.
'immodest'+'h'='immodesth'
'immodesth' with letters rearranged gives 'METHODISM'.
'of' acts as a link.
(Other definitions for methodism that I've seen before include "Christian outlook?" , "religious movement" .)