Game played by poets nursing sick setter (9)
I believe the answer is:
billiards
'game played' is the definition.
(billiards is a game)
'poets nursing sick setter' is the wordplay.
'poets' becomes 'bards' (bard is a kind of poet).
'nursing' is an insertion indicator.
'sick' becomes 'ill' (similar in meaning).
'setter' becomes 'I' (the person that set the crossword).
'ill'+'i'='illi'
'bards' placed around 'illi' is 'BILLIARDS'.
'by' acts as a link.
(Other definitions for billiards that I've seen before include "Ball game" , "Game with three balls" , "Table game at which Mary Queen of Scots excelled" , "Game played with balls on table with pockets" , "Indoor sport" .)