Coming as a c-competitor (7)
I believe the answer is:
arrival
'coming' is the definition.
(thesaurus)
'a c-competitor' is the wordplay.
'c-competitor' becomes 'rrival' ('rival' said with a stammer like 'competitor' was; 'rival' can be a synonym of 'competitor').
'a'+'rrival'='ARRIVAL'
'as' is the link.
(Other definitions for arrival that I've seen before include "Someone who's just come" , "Act of coming" , "Appearance (at a place)" , "Coming - comer" , "coming on the scene" .)