An idle sort of introduction (4-2)
I believe the answer is:
lead-in
'introduction' is the definition.
(I've seen this before)
'an idle sort' is the wordplay.
'sort' is an anagram indicator.
'an'+'idle'='anidle'
'anidle' anagrammed gives 'LEAD-IN'.
'of' acts as a link.
(Other definitions for lead-in that I've seen before include "Introduction, preamble" , "Introduction to subject" , "Introductory passage" .)