Often a moving player (5)
I believe the answer is:
piper
'moving player' is the definition.
'piper' can be an answer for 'player' (piper is a kind of player). I'm not sure about the 'moving' bit.
'often a' is the wordplay.
'often' becomes 'pi' (I can't justify this - if you can you should believe this answer much more).
'a' becomes 'per' (eg 'one a day' means 'one per day').
'pi'+'per'='PIPER'
Can you help me to learn more?
(Other definitions for piper that I've seen before include "Musician (maybe paid!)" , "Military musician" , "Bagpipes player" , "Musician (paid for a tune?)" , "One plays" .)