Peevish Le Pen jumpily interrupting a lot of criticism (9)
I believe the answer is:
splenetic
'peevish' is the definition.
(I've seen this before)
'le pen jumpily interrupting a lot of criticism' is the wordplay.
'jumpily' indicates anagramming the letters (letters jump around).
'interrupting' means one lot of letters goes inside another.
'a lot of' means to remove the last letter (most of the word but not all of it).
'criticism' becomes 'stick' (giving someone stick is criticising them).
'le'+'pen'='lepen'
'lepen' anagrammed gives 'plene'.
'stick' with its last letter taken off is 'stic'.
'plene' inserted within 'stic' is 'SPLENETIC'.
(Other definitions for splenetic that I've seen before include "Peevish" , "testy" , "Pencil set (anag.)" , "Irritable" , "Often cross" .)