They move gracefully, as now and then at first, does a runner (9)
I believe the answer is:
antelopes
'they move gracefully' is the definition.
The definition suggests an adverb but the answer is not.
'as now and then at first does a runner' is the wordplay.
'at first' suggests taking the first letters.
'does a runner' becomes 'elopes' (I am not sure about this - if you are sure you should believe this answer much more).
The first letters of 'as now then' is 'ant'.
'ant'+'elopes'='ANTELOPES'
Can you help me to learn more?
(Other definitions for antelopes that I've seen before include "Wild animals" , "Gazelles, impalas etc" , "Springboks, say" .)