Over in a group that's marooned (9)
I believe the answer is:
abandoned
'marooned' is the definition.
(I've seen this before)
'over in a group' is the wordplay.
'over' becomes 'done' (both can mean finished).
'in' indicates putting letters inside.
'group' becomes 'band' (band can mean a group of people).
'a'+'band'='aband'
'done' placed within 'aband' is 'ABANDONED'.
'that's' acts as a link.
(Other definitions for abandoned that I've seen before include "Forsook, left behind" , "Unrestrained" , "Derelict, deserted" , "Obsolete" , "Deserted - shameless" .)