Clubs undergoing trial for competition (7)
I believe the answer is:
contest
'for competition' is the definition.
(contest is a kind of competition)
'clubs undergoing trial' is the wordplay.
'clubs' becomes 'c' (abbreviation in card games).
'undergoing' becomes 'on' (on can mean experiencing or undergoing).
'trial' becomes 'test' (synonyms).
'c'+'on'+'test'='CONTEST'
(Other definitions for contest that I've seen before include "Competition or conflict" , "Match" , "Competition; dispute" , "Tournament" , "Oppose - competition" .)