One in body covering good for sport (6)
I believe the answer is:
skiing
'sport' is the definition.
(skiing is a kind of sport)
'one in body covering good' is the wordplay.
'one' becomes 'i' (Roman numeral).
'in' means one lot of letters goes inside another.
'body covering' becomes 'skin' (skin is a kind of body covering**).
'good' becomes 'g' (abbreviation).
'i' going inside 'skin' is 'skiin'.
'skiin'+'g'='SKIING'
'for' is the link.
(Other definitions for skiing that I've seen before include "Winter sports" , "Participating in a winter sport" , "Travelling over snow on runners" , "Partaking in winter sport" , "Mountain sport" .)