Boy pinching one set (4)
I believe the answer is:
laid
'set' is the definition.
('laid' can be a synonym of 'set')
'boy pinching one' is the wordplay.
'boy' becomes 'lad' (lad is a kind of boy**).
'pinching' indicates putting letters inside (taking inside).
'one' becomes 'i' (Roman numeral).
'lad' placed around 'i' is 'LAID'.
(Other definitions for laid that I've seen before include "Placed horizontally on a surface" , "(Of dining table) set" , "Flattened by wind and rain" , "Produced eggs" , "spread on a surface" .)