Split up umpires at centre (3)
I believe the answer is:
rip
'split' is the definition.
(I know that split can be written as rip)
'up umpires at centre' is the wordplay.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'at centre' indicates the central letters.
The central letters of 'umpires' are 'pir'.
'pir' in reverse letter order is 'RIP'.
(Other definitions for rip that I've seen before include "Rest in peace" , "dissolute character" , "Parting words" , "Letters appended to writing on gravestone" , "Tear violently" .)