Runner who always got the distance right (5)
I believe the answer is:
miler
'runner who always' is the definition.
'miler' can be an answer for 'runner' (miler is a kind of runner). I'm unsure of the remainder of the definition.
'the distance right' is the wordplay.
'the distance' becomes 'mile'.
'right' becomes 'r' (common abbreviation).
'mile'+'r'='MILER'
'got' is the link.
Can you help me to learn more?
(Other definitions for miler that I've seen before include "Pre-metric middle-distance runner" , "Athlete running 1,760 yards" , "Runner over a specific distance" , "one who competes in the long run" , "horse" .)