Naked runner (8)
I believe the answer is:
streaker
'naked runner' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for streaker that I've seen before include "One barely running in public" , "One can run fast" , "Rat reeks (anag.)" , "Person running without clothes" , "One who runs naughtily nude in public" .)