Thus might rugby player run from fraction (3-4)
I believe the answer is:
fly-half
'thus might rugby' is the definition.
I can't judge whether this definition defines the answer.
'player run from fraction' is the wordplay.
'player run' becomes 'fly' (I can't justify this - if you can you should believe this answer much more).
'from' is a charade indicator (letters next to each other).
'fraction' becomes 'half' (half is a kind of fraction).
'fly'+'half'='FLY-HALF'
Can you help me to learn more?
(Another definition for fly-half that I've seen is " Stand-off".)