Series on musical group first to last getting to act unrestrainedly (3,4)
I believe the answer is:
run riot
'act unrestrainedly' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'series on musical group first to last getting' is the wordplay.
'series' becomes 'run' (run is a kind of series).
'on musical group first' becomes 'rio' (I can't explain this - if you can you should believe this answer much more).
'to last' becomes 't' (I've seen this in other clues).
'getting' says to put letters next to each other.
'run'+'rio'+'t'='RUN RIOT'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for run riot that I've seen before include "Go wild" , "behave in unrestrained way" , "go crazy" , "Grow profusely (of plants)" , "Raise hell" .)