Jester extremely irritating in part -- too much backtracking (9)
I believe the answer is:
rigoletto
'jester' is the definition.
(I've seen this before)
'extremely irritating in part too much backtracking' is the wordplay.
'extremely' means to remove the middle letters.
'in' indicates putting letters inside.
'part' becomes 'role' (synonyms).
'too much' becomes 'ott' (short for 'over the top' - informal British).
'backtracking' is a reversal indicator.
'irritating' with its middle taken out is 'ig'.
'ott' backwards is 'tto'.
'ig' going into 'role' is 'rigole'.
'rigole'+'tto'='RIGOLETTO'
(Other definitions for rigoletto that I've seen before include "noted work" , "titled man" , "Verdi's hunchback jester" , "court favourite" , "Opera by Verdi" .)