Ring round with Green (6)
I believe the answer is:
callow
'green' is the definition.
(thesaurus)
'ring round with' is the wordplay.
'ring' becomes 'call' ('call' can be a synonym of 'ring'**).
'round' becomes 'o' (round can mean a round object).
'with' becomes 'w' (abbreviation).
'call'+'o'+'w'='CALLOW'
(Other definitions for callow that I've seen before include "lacking experience of life" , "Immature and inexperienced, as youth often is" , "23 [BRIGHTONIAN] actor" , "Young and inexperienced" , "Simon ---, actor; immature" .)