Scout in park descending on church (5)
I believe the answer is:
recce
'scout' is the definition.
(short for reconnoitre ie to scout out)
'park descending on church' is the wordplay.
'park' becomes 'rec' (short for recreation ground).
'descending on' means one lot of letters go next to another (in a down clue, some letters go on top of others).
'church' becomes 'CE' (abbreviation for Church of England).
'rec'+'ce'='RECCE'
'in' is the link.
(Other definitions for recce that I've seen before include "Exploratory survey (colloq.)" , "Preliminary survey" , "look round" , "Survey to obtain information" , "Reconnaissance" .)