Runners in Lusk Island (4)
I believe the answer is:
skis
'runners' is the definition.
(I know this)
'in lusk island' is the wordplay.
'in' says the answer is hidden in the clue.
'SKIS' is hidden in the letters of 'lusk island'.
(Other definitions for skis that I've seen before include "Engages in a winter sport" , "Snow runners" , "On these in slalom" , "More than one runner" , "Swoops downhill" .)