Noticed oddball penning irrational drawing (9)
I believe the answer is:
depiction
'drawing' is the definition.
(I know that depiction is a type of drawing)
'noticed oddball penning irrational' is the wordplay.
'oddball' is an anagram indicator.
'penning' indicates putting letters inside.
'irrational' becomes 'pi' (an irrational number).
'noticed' with letters rearranged gives 'dection'.
'dection' going around 'pi' is 'DEPICTION'.
(Other definitions for depiction that I've seen before include "picture" , "Representation in art" , "drawing" , "Portrayal" .)