Runner appearing in sports kit (3)
I believe the answer is:
ski
'runner' is the definition.
(something which 'runs', ie moves quickly on snow)
'in sports kit' is the wordplay.
'in' indicates the answer is hidden within the clue.
'SKI' can be found hidden inside 'sports kit'.
'appearing' acts as a link.
(Other definitions for ski that I've seen before include "Slide downhill, sportingly" , "Runner for use on snow" , "Winter sport item" , "Glide or race across snow with feet attachments" , "Slide on snow" .)