Mountain dweller to remain in climbing team (4)
I believe the answer is:
ibex
'mountain dweller' is the definition.
(type of mountain-dwelling goat)
'remain in climbing team' is the wordplay.
'remain' becomes 'be' (eg be patient, remain patient).
'in' is an insertion indicator.
'climbing' says the letters should be written backwards (in a down clue, letters climb up).
'team' becomes 'XI' (a football team, from Roman numerals for bb).
'xi' reversed gives 'ix'.
'be' going into 'ix' is 'IBEX'.
'to' is the link.
(Other definitions for ibex that I've seen before include "being nimble-footed" , "Mountain-goat" , "Sure-footed climber" , "Large-horned mountain goat" , "Pyrenean mountain goat" .)