One shows bit of rump with little hesitation? About right! (8)
I believe the answer is:
streaker
'one shows bit' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'rump with little hesitation? about right' is the wordplay.
'rump with' becomes 'steak' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'little hesitation?' becomes 'er'.
'about' is an insertion indicator.
'right' becomes 'r' (common abbreviation).
'steak'+'er'='steaker'
'steaker' enclosing 'r' is 'STREAKER'.
'of' acts as a link.
(Other definitions for streaker that I've seen before include "Exhibitionist spectator" , "Person who runs naked through a public place" , "he barely covers the distance" , "when not having a stitch" , "One who runs naughtily nude in public" .)