Change in yard after assistant referee (4)
I believe the answer is:
vary
'change' is the definition.
(synonyms)
'yard after assistant referee' is the wordplay.
'yard' becomes 'y'.
'after' is a charade indicator (letters next to each other).
'assistant referee' becomes 'var' (abbreviation for Video Assistant Referee).
'y' put after 'var' is 'VARY'.
'in' is the link.
(Other definitions for vary that I've seen before include "Make changes to" , "Undergo change" , "Differ in size" , "Be or become diverse" , "Diversify" .)