Video Assistant Referee has ultimate authority to make a change (4)
I believe the answer is:
vary
'a change' is the definition.
(I know that change can be written as vary)
'video assistant referee has ultimate authority' is the wordplay.
'video assistant referee' becomes 'VAR' (abbreviation in sports).
'has' means one lot of letters go next to another.
'ultimate' suggests the final letters.
The last letter of 'authority' is 'y'.
'var'+'y'='VARY'
'to make' acts as a link.
(Other definitions for vary that I've seen before include "Differ; change" , "Change, diverge, deviate" , "Change, amend" , "Switch" , "Diversify" .)