Religious leader shows a brashness in church (6)
I believe the answer is:
caliph
'religious leader' is the definition.
(I've seen this before)
'a brashness in church' is the wordplay.
'brashness' becomes 'lip' (I can't justify this - if you can you should believe this answer much more).
'in' indicates putting letters inside.
'church' becomes 'ch' (common abbreviation).
'a'+'lip'='alip'
'alip' inserted within 'ch' is 'CALIPH'.
'shows' acts as a link.
Can you help me to learn more?
(Other definitions for caliph that I've seen before include "Sultan of Turkey" , "Historical Muslim ruler" , "Chief Muslim ruler" , "Islamic leader" , "Muslim leader" .)