More sickly, kind of green, perhaps slalomer's heading off (7)
I believe the answer is:
peakier
'slalomer's heading off' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.
'more sickly kind of green' is the wordplay.
I cannot really see how this works, but
'green' could be 'pea' (pea green is a kind of green) and 'pea' is found within the answer.
The remaining letters 'kier' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'perhaps' acts as a link.
Can you help me to learn more?
(Other definitions for peakier that I've seen before include "In worse physical condition" , "being comparatively mountainous?" .)