Athletes needed on a sledge? (7)
I believe the answer is:
runners
'athletes' is the definition.
(runner is a kind of athlete)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for runners that I've seen before include "Joggers" , "Branches from the base of plant that produce new plants" , "Horizontal branches that produce new plants" , "Shoots" , "messengers?" .)