One who runs a small computer peripheral (8)
I believe the answer is:
sprinter
'one who runs a' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'small computer peripheral' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'computer peripheral' becomes 'printer' (I've seen this before).
's'+'printer'='SPRINTER'
Can you help me to learn more?
(Other definitions for sprinter that I've seen before include "Bolt, say" , "One moves quickly" , "one promising a fast run?" , "Person in short race" , "Athlete" .)