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 "Someone signing up for a competition", "New member or competitor", "Someone coming in", "Newcomer", "Participant in, eg, a race", "Contender", "One going in for a race or competition", "A new participant", "Contestant; starter" and "One going in for something".)