A little work in green grass pile (8)
I believe the answer is:
limerick
'a little work' is the definition.
(a short poetic work)
'green grass pile' is the wordplay.
'green' becomes 'lime' (lime is a shade of green).
'grass pile' becomes 'rick' (pile of hay).
'lime'+'rick'='LIMERICK'
'in' is the link.
(Other definitions for limerick that I've seen before include "[EDWARD LEAR] work" , "Humorous verse of 5 lines" , "Short amusing verse" , "Irish county's produced" , "Humorous poem of 5 lines, and Irish county" .)