Boy has to cite wrong part (7)
I believe the answer is:
Here is my best explanation:
'part' is the definition.
(section is a kind of part)
'boy has to cite wrong' is the subsidiary indication.
'boy' becomes 'son' ('son' can be a synonym of 'boy'**).
'has' is an insertion indicator.
'wrong' indicates anagramming the letters.
'cite' is an anagram of 'ecti'.
'son' enclosing 'ecti' is 'section'.
(Other definitions for section that I've seen before include "Division, portion", "Part, subdivision", "Cut", "surgical procedure", "Segment", "Department, division", "Distinct part", "Part; divide", "Notices (anag)" and "unit".)