Leaders ask university to umpire match next season (6)
I believe the answer is:
autumn
'season' is the definition.
(autumn is a season)
'leaders ask university to umpire match next' is the wordplay.
'leaders' suggests taking the first letters.
The first letters of 'ask university to umpire match next' is 'AUTUMN'.
(Other definitions for autumn that I've seen before include "Browning happened then" , "October's season" , "Fall for Mrs Obama" , "Fall in North America" , "Season of mists and mellow fruitfulness, according to Keats" .)