Friend in band is recovering (8)
I believe the answer is:
rallying
'recovering' is the definition.
(rallying is a kind of recovering)
'friend in band' is the wordplay.
'friend' becomes 'ally' (an ally is a friend or supporter).
'in' indicates putting letters inside.
'band' becomes 'ring' (a ring is a band of metal).
'ally' going within 'ring' is 'RALLYING'.
'is' acts as a link.
(Other definitions for rallying that I've seen before include "getting better" , "Making fun of" , "activity in cars?" , "staging recovery" , "making recovery" .)