Upon revision, sat, without competition (9)
I believe the answer is:
unopposed
'competition' is the definition.
(I know that unopposed is a type of competition)
'upon revision sat' is the wordplay.
'revision' indicates an anagram.
'sat' becomes 'posed' ('pose' can be a synonym of 'sit').
'upon' anagrammed gives 'unop'.
'unop'+'posed'='UNOPPOSED'
'without' is the link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for unopposed that I've seen before include "without query" , "Not challenged" , "so carried?" , "Nem con" , "Elected . . . . . . . . .; no other candidate" .)