Use handle wrongly — let go (9)
I believe the answer is:
unleashed
'let go' is the definition.
(I've seen this before)
'use handle wrongly' is the wordplay.
'wrongly' is an anagram indicator.
'use'+'handle'='usehandle'
'usehandle' is an anagram of 'UNLEASHED'.
(Other definitions for unleashed that I've seen before include "let go" , "Let loose" , "Freed from restraint" .)