Flea chewing sheet of paper (4)
I believe the answer is:
'sheet of paper' is the definition.
(leaf is a kind of sheet of paper)
'flea chewing' is the wordplay.
'chewing' indicates an anagram.
'flea' with letters rearranged gives 'LEAF'.
(Other definitions for leaf that I've seen before include "Page; piece of tree" , "Part of tree or book" , "needed for making a longer table" , "Part of a plant and of a book" , "Hinged or removable table flap" .)