Small church has nice deployment as a field of study (7)
I believe the answer is:
science
'a field of study' is the definition.
(science is a kind of field of study)
'small church has nice deployment' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'church' becomes 'ce' (Church of England).
'has' means one lot of letters goes inside another.
'deployment' is an anagram indicator (letters deployed in a new way).
'nice' with letters rearranged gives 'ienc'.
'ce' going around 'ienc' is 'cience'.
's'+'cience'='SCIENCE'
'as' is the link.
(Other definitions for science that I've seen before include "Biology, for example" , "Technology" , "Eg, chemistry, physics" , "Biology, perhaps?" , "Organised (search for) knowledge" .)