Sneaky round is not very good (7)
I believe the answer is:
saintly
'very good' is the definition.
'sneaky round is not' is the wordplay.
'sneaky' becomes 'sly' (I've seen this before).
'round' is an insertion indicator.
'is not' becomes 'aint' (I've seen this before).
'sly' going around 'aint' is 'SAINTLY'.
(Other definitions for saintly that I've seen before include "Very holy" , "Very virtuous" , "Beatific" , "good!" .)