A large rodent rolling over where priest stands? (5)
I believe the answer is:
altar
'where priest stands?' is the definition.
(a priest stands by the altar in a church)
'a large rodent rolling over' is the wordplay.
'large' becomes 'l'.
'rodent' becomes 'rat' (rat is a kind of rodent).
'rolling over' says the letters should be written in reverse.
'rat' in reverse letter order is 'tar'.
'a'+'l'+'tar'='ALTAR'
(Other definitions for altar that I've seen before include "High ceremonial table" , "Table for sacrifice" , "Sacrificial structure" , "Sacrificial table" , "Focal point for Mass" .)