Dusk has time for sport (8)
I believe the answer is:
eventing
'for sport' is the definition.
(I've seen this before)
'dusk has time' is the wordplay.
'dusk' becomes 'evening' (I've seen this before).
'has' means one lot of letters goes inside another.
'time' becomes 't' (abbreviation).
'evening' enclosing 't' is 'EVENTING'.
(Other definitions for eventing that I've seen before include "Sport consisting of dressage, cross country and show jumping" , "Equestrian competition" , "A three-phase equestrian sport" .)