Rival clubs promote changes covering it (10)
I believe the answer is:
competitor
'rival' is the definition.
('competitor' can be a synonym of 'rival')
'clubs promote changes covering it' is the wordplay.
'clubs' becomes 'c' (abbreviation used in card games such as bridge).
'changes' is an anagram indicator.
'covering' indicates putting letters inside.
'c'+'promote'='cpromote'
'cpromote' is an anagram of 'competor'.
'competor' enclosing 'it' is 'COMPETITOR'.
(Other definitions for competitor that I've seen before include "rival trader?" , "Sporting contest entrant" .)