One on the wing that races linesman (5)
I believe the answer is:
homer
'linesman' is the definition.
(Homer is an example)
'one on the wing that races' is the wordplay.
'one on' says to put letters next to each other.
'the wing' becomes 'r' (r is abbreviation for right).
'that races' becomes 'home' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'r' put after 'home' is 'HOMER'.
Can you help me to learn more?
(Other definitions for homer that I've seen before include "Ancient Greek author" , "Measure < of poet's" , "Ancient Greek poet" , "makes round trip by air" , "Blind man" .)