The umpire men finally chose thus (9)
I believe the answer is:
therefore
'thus' is the definition.
('therefore' can be a synonym of 'thus')
'the umpire men finally chose' is the wordplay.
'umpire' becomes 'ref' (I've seen this before).
'men' becomes 'or' (I've seen this in other clues).
'finally' indicates one should take the final letters.
The final letter of 'chose' is 'e'.
'the'+'ref'+'or'+'e'='THEREFORE'
(Other definitions for therefore that I've seen before include "has a triangular formation in maths?" , "It follows" , "In consequence" , "Consequently - for that reason" , "Thus" .)