Friend nabbed by gang is getting better (8)
I believe the answer is:
'is getting better' is the definition.
(I've seen this before)
'friend nabbed by gang' is the wordplay.
'friend' becomes 'ally' (an ally is a friend or supporter).
'nabbed by' indicates putting letters inside (nab can mean to steal or take possession of).
'gang' becomes 'ring' (synonyms).
'ally' inserted within 'ring' is 'RALLYING'.
(Other definitions for rallying that I've seen before include "Reviving" , "staging recovery" , "activity in cars?" , "Making fun of" , "getting better" .)