Favoured umpire slipped up after start of play (9)
I believe the answer is:
preferred
'favoured' is the definition.
('prefer' can be a synonym of 'favour')
'umpire slipped up after start of play' is the wordplay.
'umpire' becomes 'ref' (short for referee).
'slipped up' becomes 'erred' (I've seen this in another clue).
'after' says to put letters next to each other.
'start of' suggests taking the first letters.
The first letter of 'play' is 'p'.
'ref'+'erred'='referred'
'referred' after 'p' is 'PREFERRED'.
(Other definitions for preferred that I've seen before include "Chose before others" , "choice" , "Was partial to" , "singled out" , "Liked better" .)