A spell of unrestrained activity (5)
I believe the answer is:
spree
'a spell of unrestrained activity' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for spree that I've seen before include "booze-up?" , "Overindulgent bout" , "Self-indulgent bout" , "night on the razzle?" , "orgy" .)