Tea service one knocked over (5)
I believe the answer is:
assam
'tea' is the definition.
(I've seen this before)
'service one knocked over' is the wordplay.
'service' becomes 'mass' (kind of church service).
'one' becomes 'a' (a thing is one thing).
'knocked over' is a reversal indicator.
'mass'+'a'='massa'
'massa' reversed gives 'ASSAM'.
(Other definitions for assam that I've seen before include "North-east Indian tea state" , "region out east" , "Tea-growing region" , "part of India" , "Variety of tea" .)