Leave a group with no backing (7)
I believe the answer is:
abandon
'leave' is the definition.
(to abandon is to leave or desert)
'a group with no backing' is the wordplay.
'group' becomes 'band' (band can mean a group of people).
'with' says to put letters next to each other.
'backing' is a reversal indicator.
'no' backwards is 'on'.
'a'+'band'+'on'='ABANDON'
(Other definitions for abandon that I've seen before include "Leave behind - licentiousness" , "Lack of constraint" , "Leave high and dry" , "Junk" , "a complete lack of restraint" .)