Ability of a runner to get £50 (5)
I believe the answer is:
skill
'ability' is the definition.
(I know that ability is a type of skill)
'a runner to get ps50' is the wordplay.
'a runner' becomes 'ski' (something which 'runs', ie moves quickly on snow).
'to get' says to put letters next to each other.
'ps50' becomes 'll' (I am not sure about this - if you are sure you should believe this answer much more).
'ski'+'ll'='SKILL'
'of' is the link.
Can you help me to learn more?
(Other definitions for skill that I've seen before include "facility" , "Knack" , "Aptitude" , "Special ability" , "Expertise; art" .)