Article I stuffed into leotard I designed (9)
I believe the answer is:
editorial
'article' is the definition.
(I know that editorial is a type of article)
'i stuffed into leotard i designed' is the wordplay.
'stuffed into' is an insertion indicator.
'designed' indicates an anagram (designed with the letters).
'leotard'+'i'='leotardi'
'leotardi' anagrammed gives 'edtorial'.
'i' put within 'edtorial' is 'EDITORIAL'.
(Other definitions for editorial that I've seen before include "Chief newspaper article" , "Statement of a newspaper's opinion" , "matter of opinion" , "Newspaper article giving the editor's opinions" , "Newspaper item" .)