Watched rival? United? (6)
I believe the answer is:
viewed
'watched' is the definition.
('view' can be a synonym of 'watch')
'rival? united?' is the wordplay.
'rival?' becomes 'vie' (rivalling is a kind of vying).
'united?' becomes 'wed' (united in marriage).
'vie'+'wed'='VIEWED'
(Other definitions for viewed that I've seen before include "seen on TV" , "Considered or deemed to be" , "Considered or looked at" , "Observed" , "Saw" .)