Competitor in event ran tiredly (7)
I believe the answer is:
entrant
'competitor' is the definition.
(thesaurus)
'in event ran tiredly' is the wordplay.
'in' indicates the answer is hidden within the clue.
'ENTRANT' can be found hidden inside 'event ran tiredly'.
(Other definitions for entrant that I've seen before include "Newcomer" , "One going in for exam" , "Participant in competition" , "Who goes in" , "Candidate" .)