Behave wildly and without restraint (3,4)
I believe the answer is:
run riot
'behave wildly and without restraint' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for run riot that I've seen before include "Behave wildly and without restraint" , "Lose control" , "Of mob, throw off all restraint" , "behave in unrestrained way" , "high-scoring test match" .)