Big sea bird — there’s three fewer than expected on the green (9)
I believe the answer is:
albatross
This clue could be a double definition.
'big sea bird' is the first definition.
'albatross' can be an answer for 'bird' (albatross is a kind of bird). I am unsure of the 'big sea' bit.
'three fewer than expected on the green' is the second definition.
(three under par in golf)
'there's' acts as a link.
Can you help me to learn more?
(Other definitions for albatross that I've seen before include "not achieved by many golfers" , "Long-winged sea-bird, a constant burden" , "that golfer with a hole in one might register?" , "Large oceanic bird" , "Coleridge's marine bird." .)