Private enters petitions for new recruits (9)
I believe the answer is:
beginners
'new recruits' is the definition.
(people who've only just been recruited)
'private enters petitions' is the wordplay.
'private' becomes 'inner' (as in one's private or inner thoughts).
'enters' is an insertion indicator.
'petitions' becomes 'begs' (petition can mean to beg or plead).
'inner' inserted within 'begs' is 'BEGINNERS'.
'for' is the link.
(Other definitions for beginners that I've seen before include "Those at an early stage of learning" , "Novices" .)