As worn by the runner on the right? (5)
I believe the answer is:
skirt
'as' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'worn by the runner on the right?' is the wordplay.
'worn by' means one lot of letters goes inside another (inserted letters are worn or displayed by others).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'runner' becomes 'ski' (something which 'runs', ie moves quickly on snow).
'on' is a charade indicator (letters next to each other).
'the right?' becomes 'R' (common abbreviation).
't' put after 'ski' is 'skit'.
'skit' going around 'r' is 'SKIRT'.
Can you help me to learn more?
(Other definitions for skirt that I've seen before include "Fringe" , "Circumvent" , "Item of female apparel" , "Female garment" , "Go round; garment" .)