Enthusiastic about, if not moving without force (4)
I believe the answer is:
into
'enthusiastic about' is the definition.
(into can mean interested in or enthusiastic about)
'not moving without force' is the wordplay.
'moving' indicates an anagram (letters are moved around).
'without' means one lot of letters goes inside another ('without' can be similar in meaning to 'outside').
'force' becomes 'i' (I can't justify this - if you can you should believe this answer much more).
'not' anagrammed gives 'nto'.
'nto' placed around 'i' is 'INTO'.
'if' is the link.
Can you help me to learn more?
(Other definitions for into that I've seen before include "ignition regularly missing" , "Taking a lively and active interest in (colloq.)" , "To a position within" , "Fascinated by" , "Showing enthusiasm for" .)