Natter about including new beginner (7)
I believe the answer is:
Here is my best explanation:
'beginner' is the definition.
(entrant is a kind of beginner)
'natter about including new' is the subsidiary indication.
'about' indicates anagramming the letters.
'including' means one lot of letters goes inside another.
'new' becomes 'n'.
'natter' with letters rearranged gives 'entrat'.
'entrat' placed around 'n' is 'entrant'.
(Other definitions for entrant that I've seen before include "A new participant", "Contender", "One going in for something", "Contestant; starter", "Someone taking part in a competition", "Someone signing up for a competition", "Participant in, eg, a race", "New participant", "One taking part in a race or competition" and "Competitor, contestant".)