One running small peripheral device (8)
I believe the answer is:
sprinter
'one running' is the definition.
(I've seen this before)
'small peripheral device' is the wordplay.
I cannot quite see how this works, but
'small' could be 's' (abbreviation - e.g. clothes size) and 's' is found in the answer.
'device' could be 'printer' (printer is a kind of device) and 'printer' is located in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for sprinter that I've seen before include "Athlete" , "Bolt, say" , "one in the 100 metres" , "Person in short race" , "Short-distance runner" .)