Robin arrested, stupidly nicking book (9)
I believe the answer is:
redbreast
'robin' is the definition.
('redbreast' can be a synonym of 'robin')
'arrested stupidly nicking book' is the wordplay.
'stupidly' indicates anagramming the letters.
'nicking' indicates putting letters inside (I've seen this in other clues).
'book' becomes 'b'.
'arrested' with letters rearranged gives 'redreast'.
'redreast' going around 'b' is 'REDBREAST'.
(Other definitions for redbreast that I've seen before include "Flapper" , "Bird" , "Type of robin" , "One tweets" .)