A competitor, about mid-afternoon, coming (7)
I believe the answer is:
arrival
'coming' is the definition.
(thesaurus)
'a competitor about mid-afternoon' is the wordplay.
'competitor' becomes 'rival' ('rival' can be a synonym of 'competitor'**).
'about' says to put letters next to each other.
'mid' means to look at the middle letters.
The middle of 'afternoon' is 'r'.
'rival' after 'r' is 'rrival'.
'a'+'rrival'='ARRIVAL'
(Other definitions for arrival that I've seen before include "Entry" , "Someone who's just come" , "Appearance, entrance" , "Appearance (at a place)" , "coming on the scene" .)