Spotted copper nabbing group in outdoor building (9)
I believe the answer is:
splotched
'spotted' is the definition.
(splotching is a kind of spotting)
'copper nabbing group in outdoor building' is the wordplay.
'copper' becomes 'PC' (police constable).
'nabbing' means one lot of letters goes inside another (nab can mean to capture or arrest).
'group' becomes 'lot'.
'in' means one lot of letters goes inside another.
'outdoor building' becomes 'shed' (garden shed).
'pc' placed around 'lot' is 'plotc'.
'plotc' put into 'shed' is 'SPLOTCHED'.
(Other definitions for splotched that I've seen before include "Roughly marked" , "Spotted, splashed" .)