Going round the fields is pure delight (8)
I believe the answer is:
pleasure
'delight' is the definition.
('pleasure' can be a synonym of 'delight')
'going round the fields is pure' is the wordplay.
'going round' is an insertion indicator.
'the fields' becomes 'leas' (I've seen this before).
'leas' inserted inside 'pure' is 'PLEASURE'.
(Other definitions for pleasure that I've seen before include "Delectation, delight" , "diversion" , "'Enjoyment, delight (8)'" , "Delight, joy" , "Feeling of enjoyment or satisfaction" .)