Eels are wriggling free (7)
I believe the answer is:
release
'free' is the definition.
(to release someone is to free them)
'eels are wriggling' is the wordplay.
'wriggling' indicates an anagram (letters wriggle or move about).
'eels'+'are'='eelsare'
'eelsare' is an anagram of 'RELEASE'.
(Other definitions for release that I've seen before include "Free - delivery" , "press announcement" , "put out" , "Set free - publish" , "Let go" .)