Newcomer runs into a challenger (7)
I believe the answer is:
arrival
'newcomer' is the definition.
(thesaurus)
'runs into a challenger' is the wordplay.
'runs' becomes 'r' (cricket abbreviation).
'into' indicates putting letters inside.
'challenger' becomes 'rival' (synonyms).
'a'+'rival'='arival'
'r' put within 'arival' is 'ARRIVAL'.
(Other definitions for arrival that I've seen before include "Act of coming" , "Appearance (at a place)" , "Entry" , "Achievement of destination" , "coming on the scene" .)