Repeatedly clean up fluffy ball (6)
I believe the answer is:
pompom
'fluffy ball' is the definition.
(a pompom is a decorative fluffy ball)
'repeatedly clean up' is the wordplay.
'repeatedly' says to double the letters.
'clean' becomes 'mop' (mopping is a kind of cleaning).
'up' is a reversal indicator (in down clue: letters go upwards).
'mop' in reverse letter order is 'pom'.
'pom' duplicated is 'POMPOM'.
(Other definitions for pompom that I've seen before include "Top decoration" , "Decorative ball of tufted wool" , "Cheerleader's ball of material" , "Hat ornament" , "fluffy decoration" .)