Left group, one used in commercial (9)
I believe the answer is:
abandoned
'left' is the definition.
(abandoning is a kind of leaving)
'group one used in commercial' is the wordplay.
'group' becomes 'band' (band is a kind of group).
'used in' means one lot of letters goes inside another.
'commercial' becomes 'ad'.
'band'+'one'='bandone'
'bandone' going into 'ad' is 'ABANDONED'.
(Other definitions for abandoned that I've seen before include "Dropped" , "Deserted - shameless" , "Rejected" , "Crazy!" , "No longer inhabited and left desolate" .)