Try to stop each victory of US (9)
I believe the answer is:
endeavour
'try' is the definition.
(endeavouring is a kind of trying)
'stop each victory of us' is the wordplay.
'stop' becomes 'end' ('end' can be a synonym of 'stop'**).
'each' becomes 'ea'.
'victory' becomes 'v'.
'of us' becomes 'our' (I've seen this before).
'end'+'ea'+'v'+'our'='ENDEAVOUR'
'to' acts as a link.
(Other definitions for endeavour that I've seen before include "Try hard (to achieve)" , "Captain Cook's first ship - DCI Morse's first name" , "Industrious effort" , "hard work" , "Make a serious effort" .)