Jumper to go around and around and win by one of the shortest of margins
I believe the answer is:
rollneck
'one of the shortest of margins' is the definition.
The definition suggests a singular noun which matches the answer.
'jumper to go around and around and win' is the wordplay.
I cannot quite understand how this works, but
'go' could be 'roll' (rolling is a kind of going) and 'roll' is found in the answer.
'around' could be 'c' (abbreviation for 'circa') and 'c' is found in the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is found within the answer.
This may be the basis of clue (or it may be nonsense).
'by' acts as a link.
Can you help me to learn more?
(Other definitions for rollneck that I've seen before include "Type of sweater" , "Type of woollen" , "Type of turned-down collar on a garment" .)