Grass always covered in the opening equestrian competition (5-3,5)
I believe the answer is:
three-day event
'equestrian competition' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for three-day event that I've seen before include "Equestrian competition involving several skills" , "Horse-riding competition" , "Dressage, cross-country and showjumping" , "Equestrian competition comprising several disciplines" .)