Update umpire concerning his having missed one over (7)
I believe the answer is:
refresh
'update' is the definition.
(I've seen this in another clue)
'umpire concerning his having missed one over' is the wordplay.
'umpire' becomes 'ref' (short for referee).
'concerning' becomes 're' (both can mean on a particular topic).
'having missed' indicates named letters should be taken away.
'one' becomes 'i' (Roman numeral).
'over' says the letters should be written in reverse.
'his' with 'i' taken out is 'hs'.
'hs' backwards is 'sh'.
'ref'+'re'+'sh'='REFRESH'
(Other definitions for refresh that I've seen before include "Give new strength to" , "Give new energy to" , "Invigorate, make new again" , "Stimulate as by reminding, or top up drink" , "perk up!" .)