Bar that's shut up when clergyman enters (7)
I believe the answer is:
prevent
'bar' is the definition.
(I know that bar is a more specific form of block)
'shut up when clergyman enters' is the wordplay.
'shut up' becomes 'pen' (pen can mean to shut in or enclose).
'when' becomes 't' (I can't explain this - if you can you should believe this answer much more).
'clergyman' becomes 'rev' (short for reverend).
'enters' indicates putting letters inside.
'pen'+'t'='pent'
'pent' placed around 'rev' is 'PREVENT'.
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for prevent that I've seen before include "Keep from arising" , "Bar" , "Stop from happening" , "Stop, avert" , "Stop (an action)" .)